clear-after.html

<style>
  .container:after {
    content: '';
    clear: both;
  }
  
  img { float: left }
</style>

<div class="container">
  <img src=".." alt="float element" />
  <p>blah blah blah...</p>
</div>

clear.html

<style>
  img { float: left }
  .null { 
    display: block;
    clear: both 
  }
</style>

<div class="container">
  <img src=".." alt="float element" />
  <p>blah blah blah...</p>
  <span class="null"></span>
</div>

float.html

<style>
  .dv1 { float: left }
  .dv2 { float: right }
</style>

<div class="dv1">dv1</div>
<div class="dv2">dv2</div>
<p>floating blah blah blah...</p>