Select APC and install that.WHM >> Software >> Module Installers >> PHP Pecl
Once its installed check if the extension is added, if not add apc.so to php.ini
To configure caching, login to apc admin panel. First you need to copy "apc.php" to web accessible location
cp /usr/local/lib/php/apc.php /home/username/public_html/
Edit /home/username/public_html/apc.php and add the admin loginschown user:user /home/username/public_html/apc.php
vi /home/username/public_html/apc.php