You can write html directly in a .php file.
To enter php mode, write code inside a self closing <?php code here ?> tag.
In a .php file:
<p>This code will be delivered as it is</p>
<?php
echo "<p>This code is interpreted by php and turned into HTML</p>;"
?>
If used in the cli, it’s common practice to not close the <?php tag
<?php
// code here with no closing tag
Use // or /* text */
// Comment
/* multi line
comment */
<?php
echo "one " . "two";
<?php
$my_variable = "hello";
echo $ my_variable;