Install on Unix/cn
At the moment, the FreeCAD team only provides installers for 32bit Debian and Ubuntu systems, but some members of the FreeCAD users community also provide custom installers for other Linux flavors. Please have a look at the Download page to see what is currently availible.
Installing on Debian/Ubuntu systems
Once you downloaded the .deb corresponding to your system version, if you have the Gdebi package installed (usually it is), you just need to navigate to where you downloaded the file, and double-click on it. The necessary dependencies will be taken care of automatically by your system package manager. Alternatively you can also install it from the terminal, navigating to where you downloaded the file, and type:
sudo dpkg -i Name_of_your_FreeCAD_package.deb
changing Name_of_your_FreeCAD_package.deb by the name of the file you downloaded.
After you installed FreeCAD, a startup icon will be added in the "Graphic" section of your Start Menu.
Installing on other Linux/Unix systems
Unfortnately, at the moment, no precompiled package is availible for other Linux/Unix systems,so you will need to compile FreeCAD yourself.