There is an apc_add() built in function in php and i tried to use it
but it show me this error message below,

Fatal error: Call to undefined function apc_add() in /home/travels/public_html/functions/apc_add.php on line 3

I also noticed that it has a requirements like this below
(PECL apc:3.0.13-3.0.14)

what does this mean?

Do i need to install PECL on the server. any complete and detail explanation
for this please.

Thank you very much in advance.