I suffered learning Git through command line, GitX and later SmartGit in 2010. Despite being much more comfortable with git in Terminal now, Tower is the best GUI out there. And it's constantly improving.
If you want to learn how to use Git, there is nothing better to start with than GitHub's excellent Help. The guys at GitHub offer an online hosting service for Git repositories and they understand that their interest lies in making Git easier to understand for anyone.
In that spirit, they recently released GitHub for Mac, and excellent and simple graphical user interface to Git that removes much of the confusion for beginners.
I highly recommend it if you have no concept of how to use Git and you don't want to commit the time to learn it with the command line. It's a tedious yet ultimately rewarding task that not everyone can afford.
If you want to learn Git inside and out, Scott Chacon's book Pro Git is the place to start. It's free, and Scott's not the GitHub CIO because he buys everyone drinks. Alright, maybe that's why, but he's also damn knowledgeable about Git and its inner workings.