The instructions here are adapted from http://book.git-scm.com/2_installing_git.html
sudo apt-get install git-core
sudo yum install git-core
There are several ways to install git on Mac. The easiest is to simply download the OS X installer (git-osx-installer). If you have MacPorts installed, you can also do:
sudo port install git-core
If you have Fink installed, you can do:
sudo apt-get install git
In addition, you may want to use a GUI to manage your git repositories. A good example of a free Mac GUI is GitX. Other (non-free) examples include Tower and SourceTree. GitHub have also recently released GitHub for Mac.