I think before posting a thread for this, you should understand the syntax of the programming language you are learning. PHP syntax and semantics - Wikipedia, the free encyclopedia

open parenthesis (

Close parenthesis )

Its used to define a function

Parenthesis is used to create a function, this is for example:

if (filter_var($int, FILTER_VALIDATE_INT, array("options" => array("min_range"=>$min, "max_range"=>$max))) === false) {
echo("Variable value is not within the legal range");

They're used to create/define a function.

PHP is a procedural and object oriented language for coding webpage markup text to be transformed into html format.The PHP syntax and semantics are the format and the related meaning of the text and symbols in the PHP programming language.
The open parenthesis in php is:
(
The close parenthesis in php is:
)

ex:
mysql_connect("localhost","db_username","db_passwo rd")