Download the latest version of git from here: http://git-scm.com
Graphical front ends can be found here: http://git-scm.com/download/gui/mac
Read more about git here (the first 3 chapters are enough to get going): http://git-scm.com/book/en/Git-Basics-Recording-Changes-to-the-Repository
Here's a git cheatsheet: http://cloud.github.com/downloads/AlexZeitler/gitcheatsheet/gitcheatshee...
Put the following in a file called .gitignore in your home directory:
*.[oa] *.mxo *.mxe *.class *.objinfo.txt *.tar.gz *.zip *.def *~ \#\*\# xcuserdata .DS_Store build build-gcc *.pbxuser *.mode1v3 *.mode2v3 *.perspectivev3 !default.pbxuser !default.mode1v3 !default.mode2v3 !default.perspectivev3 !xcshareddata