Creating basic Shortcodes in WordPress

shortcodes.php

<?php
// create your shortcode function
function guru_my_shortcode() {

    // do something here

    // return text you want to display
    return $output;
}

// register all shortcodes
function guru_shortcodes() {
    add_shortcode( 'your-handle', 'guru_my_shortcode' );
}
add_action( 'init', 'guru_shortcodes' );