Creating custom reports using qweb in Odoo

create_custom_report_using_qweb_odoo.xml

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
   <data>

      <!-- Add the report to the XML file responsible for reports -->
      <report id="report_unique_xml_id"
              model="your.model.name"
              string="Report Name"
              name="module_name.report_name"
              file="module_name.report_unique_xml_id"
              report_type="qweb-pdf"
      />

      <!-- setting paper format for report -->
      <record id="paper_format_unique_name_related_to_report" model="report.paperformat">
         <field name="name">Report Name</field>
         <field name="default" eval="True" />
         <field name="format">A4</field>
         <field name="page_height">0</field>
         <field name="page_width">0</field>
         <field name="orientation">Portrait</field>
         <field name="margin_top">3</field>
         <field name="margin_bottom">2</field>
         <field name="margin_left">2</field>
         <field name="margin_right">2</field>
         <field name="header_line" eval="False" />
         <field name="header_spacing">3</field>
         <field name="dpi">80</field>
      </record>

      <!-- binding paper format with qweb report-->
      <record id="module_name.report_unique_xml_id" model="ir.actions.report.xml">
         <field name="paperformat_id" ref="module_name.paper_format_unique_name_related_to_report" />
      </record>

      <template id="report_name">
         <style>.report_border {
              border: 1px solid black;
            }
            .none_border {
              border: none;
              border-top: none;
            }
            .report_border > thead > tr > th,
            .report_border > tbody > tr > th,
            .report_border > thead > tr > td,
            .report_border > tbody > tr > td {
              border: 1px solid black !important;
            }</style>

         <!-- "docs" contains (your.model.name) which you have defined above
         now you can access fields from docs for example data.name, data.contact_no etc
         -->
         <t t-foreach="docs" t-as="data">
            <t t-call="report.html_container">
               <div class="page">
                  <div class="oe_structure" />
                  <div class="text-center">
                     <h3>
                        <b>Report Title Goes Here</b>
                     </h3>
                  </div>
                  <div>
                     <table class="table report_border">
                        
                        <!-- getting values from model in QWEB--> 
                        <tr>
                           <th style="width: 25%; font-size:18px;">Name</th>
                           <td style="font-size:20px;">
                              <span t-field="data.name" />
                           </td>
                        </tr>

                        <!-- how to define conditional statements in QWEB -->
                        <tr>
                           <th style="width: 25%; vertical-align: top; font-size:18px;">Personal</th>
                           <td>
                              <table class="table report_border">
                                 <tr>
                                    <t t-if="data.contact_number1 == False">
                                       <td style="font-size:17px;">
                                          <b>Contact No :</b>
                                          <span t-field="data.contact_number2" />
                                       </td>
                                    </t>
                                    <t t-if="data.contact_number2 == False">
                                       <td style="font-size:17px;">
                                          <b>Contact No :</b>
                                          <span t-field="data.contact_number1" />
                                       </td>
                                    </t>
                                    <t t-if="data.contact_number1 and data.contact_number2 != False">
                                       <td style="font-size:17px;">
                                          <b>Contact No:</b>
                                          <li style="list-style-type: none;">
                                             <span t-field="data.contact_number1" />
                                             <br />
                                          </li>
                                          <li style="list-style-type: none;">
                                             <span t-field="data.contact_number2" />
                                          </li>
                                       </td>
                                    </t>
                                 </tr>
                              </table>
                           </td>
                        </tr>

                        <!-- getting one2many relational fields in QWEb-->
                        <!-- how to use nested loops in QWEb-->
                        <tr>
                           <th style="width: 25%; vertical-align: top; font-size:18px;">Experience</th>
                           <td style="font-size:17px;">
                              <table class="table report_border">
                                 <th style="width: 10%;">Duration</th>
                                 <th style="width: 10%;">Job Title</th>
                                 <th style="width: 10%;">Institution</th>
                                 <tbody>
                                    <t t-foreach="data" t-as="experience">
                                       <t t-foreach="experience.one2many_field" t-as="duration">
                                          <tr>
                                             <td>
                                                <p>
                                                   <t t-if="duration.curr_work == False">
                                                      <span t-field="duration.date_from" t-field-options='{"format": "d-MMM-y"}' />
                                                      to
                                                      <span t-field="duration.date_to" t-field-options='{"format": "d-MMM-y"}' />
                                                      <br />
                                                   </t>
                                                   <t t-if="duration.curr_work == True">
                                                      <span t-field="duration.date_from" t-field-options='{"format": "d-MMM-y"}' />
                                                      To Present
                                                   </t>
                                                </p>
                                             </td>
                                          </tr>
                                       </t>
                                    </t>
                                 </tbody>
                              </table>
                           </td>
                        </tr>
                         
                        <!-- how to show data in ordered list in QWEB--> 
                        <tr>
                           <th style="width: 25%; vertical-align: top; font-size:18px;">Ordered List</th>
                           <td style="font-size:17px;">
                              <t t-foreach="data.one2many_field" t-as="honor">
                                 <li style="list-style-type: none;">
                                    <p t-field="honor.name" />
                                 </li>
                              </t>
                           </td>
                        </tr>
                         
                        <!-- create table inside table row in QWEB--> 
                        <tr>
                           <th style="width: 25%; vertical-align: top; font-size:18px;">Supervision</th>
                           <td style="font-size:17px;">
                              <table class="table report_border">
                                 <th style="width: 10%;">Year</th>
                                 <th style="width: 10%;">Degree</th>
                                 <th style="width: 10%;">Name</th>
                                 <tbody>
                                    <t t-foreach="data" t-as="supervision">
                                       <t t-foreach="supervision.one2many_field" t-as="year">
                                          <tr>
                                             <td>
                                                <p t-esc="year.year" />
                                             </td>
                                             <td>
                                                <p t-esc="year.degree" />
                                             </td>
                                             <td>
                                                <p t-esc="year.name" />
                                             </td>
                                          </tr>
                                       </t>
                                    </t>
                                 </tbody>
                              </table>
                           </td>
                        </tr>
                     </table>
                  </div>
               </div>
            </t>
         </t>
      </template>
   </data>
</openerp>

Read more in detail: https://learnopenerp.blogspot.com/2020/08/create-custom-report-in-odoo-using-qweb.html