There are different ways of installing software on your Raspberry Pi, depending on where the source of the software lives.

The most common is through command line tool APT (Advanced Packaging Tool), and there is the Pi Store - the Raspberry Pi's own user contributed app store. Also some software can be installed using other package managers.

• APT
  • Use apt-get install to install software from the Raspbian archives
• Pi Store
  • The Pi Store is an application found on the Raspbian desktop, which provides a graphical interface to installing community contributed software and games
• Python
  • Some Python software can be installed using a Python package manager such as pip
• Ruby
  • Some Ruby software can be installed with Ruby's package manager ruby gems