Require function is similar to include() function the only difference is that include() function will continue code execution after giving a warning message, but require() function will end the code execution after giving a Fatal error message

    <?php
    require ("test1.php");
    echo "HI";
    ?>

    Fatal error: main(): Failed opening required test1.php

In the above example the "Require()" structure is giving a Fatal Error message as test1.php is not existent and stops the execution of the code below, but if the "Include" structure is used it will give a warning message and continue the processing to display "HI"