It is a little more complicated than that in practice, but not much - the string delimiter needs to be by itself on a line, in the very first column. That is, you cannot add spacing or tabs around it.
Take a look at this example:
$mystring = <<<EOT
This is some PHP text.
It is completely free
I can use "double quotes"
and 'single quotes',
plus $variables too, which will
be properly converted to their values,
you can even type EOT, as long as it
is not alone on a line, like this:
There are several key things to note about heredoc, and the example above:
You can use anything you like; "EOT" is just an example
You need to use <<< before the delimiter to tell PHP you want to enter heredoc mode
Variable substitution is used in PHP, which means you do need to escape dollar symbols - if you do not, PHP will attempt variable replacement.
You can use your delimiter anywhere in the text, but not in the first column of a new line
At the end of the string, just type the delimiter with no spaces around it, followed by a semi-colon to end the statement
Without heredoc syntax, complicated string assignments can quickly become very messy. Heredoc is not used all that often in the wild - very often you will wish it were used more, because too many scripts you will come across have messy code as a result of not using heredoc!