Advanced Packaging Tool (APT) is a free piece of software which allows the easy install, removal and configuration of applications on Debian based linux distros.
Installing software with APT is usually as simple as apt-get install software-name. for example if you wanted to install Apache2 you would open a terminal and type apt-get install apache2
Removing a program is just as easy with the apt-get remove option. For example to remove your webserver, you could run apt-get remove apache2. You may find that some config files still exist after the removal.