Caching is one of the most powerful features in PHP. Here is the step to install.
First install php5 and other required package with sudo Authentication

sudo apt-get install apache2-threaded-dev php5-dev php-pear make

Then install APC package

sudo pecl install apc

if there is asking some yes/no just write yes and the Last step add installed extension in php configuration like this

sudo vim /etc/php5/conf.d/apc.ini

and then insert following code in opened file “apc.ini”

 extension=apc.so