I won't claim that this is the best version control software out there, but it works well for me. I use Git as a backend (read more about it on Wikipedia if you'd like -- Linus Torvolds started it) and SmartGit as my user interface. It allows me to commit changes with comments or revert to old versions. I can also see the differences between versions and track file history (branches, etc.).
As your next step, you can check out some of the screenshots I've posted below (stolen from SmartGit's screenshots page) or read another review.
|Directory and file list|
|Graphical change log|
|Differences between two files|