Here echo is used to print something in output console. $ is used with variable, in PHP all variables are precedes with $ sign, you have to use $ with all variables. Every line of code must be ended with semicolon (;).
Note that every PHP Script must start with <?php and ended with ?>, this means whole script must be written between <?php …. ?>.
<?php $a= "Hello World!"; echo $a."<br>"; ?>