Inserting PHP Code into HTML

Let's say we have some HTML code:

html<p>text</p>

We can insert PHP code inside this code:

html<p><?php 'any code' ?></p>

Let's, for example, output some text:

html<p><?php echo 'text'; ?></p>

And now the result of the function:

html<p><?php echo sqrt(4); ?></p>

html<p></p>