PHP Questions!

<?php
if ($expression) {
    ?>
    <strong>This is true.</strong>
    <?php
} else {
    ?>
    <strong>This is false.</strong>
    <?php
}
?>

I am confused by this code.
Can anyone explain to me what happens if $expression is true? false?

i heard on the streets that php fags call it "echo" or some nonsense like that