Did you read from page 111 in the handbook? That is about as best as it can be explained?
It is also called HEREDOC
Heredoc text behaves just like a double-quoted string, without the double quotes
// here is a string
$howdy= "Howzit my china! Are you well?
Come visit me!";
//here it is heredco style
$howdy =
<<<EOD
Howzit my china! Are you well?
Come visit me!
EOD;
Why use it?
Heredoc is rarely used as the day by day usage is more complicated as creating strings with quotes or double quotes.
So forget about it for now - but now about it.