Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Compiling from source is the only way to use a lot of free software that your Linux package manager can't find, ready for download, in an Internet repository. Thankfully, compiling is often much easier than you may think.
In this post, I'll explain the most common way to install from sources on Linux -- suggesting, as a practical example, that you may replicate on your computer an actual compilation of the AbiWord 3.0 word processor on a Fedora 17 x86_64 box. My explanation is valid on most other distributions, as long as you change the "yum" parts with equivalent invocations of their package manager. Also, remember that only "yum" and (if installing to system folders) "make install" should be ran as root, and use your normal account for all the other steps.