Homebrew allows you to easily install hundreds of open-source tools. The full instructions are available on the Homebrew Wiki, but you should only need to run the command that’s listed at the bottom of the Homebrew site:
ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
Follow the on screen instruction. Remember that Terminal doesn't provide feedback when writing your password.
After the instalation is done, run brew doctor to check that there were no problems. If everything is ok, you should see:
$ brew doctor
Your system is ready to brew.
Unless otherwise specified in the output, you can move on to installing git.
If you get Warning: /usr/bin occurs before /usr/local/bin when running brew doctor, run the command below, as recommended by Homebrew:
$ echo 'export PATH="/usr/local/bin:$PATH"' >> ~/.bash_profile
Quit & relauch Terminal, then run brew doctor again. You should be ready to brew.
If you get Error: No such file or directory - /usr/local/Cellar when running brew doctor, create the Cellar folder:
$ sudo mkdir /usr/local/Cellar
Quit & relauch Terminal, then run brew doctor again. You should be ready to brew.
For other common problems with Homebrew, check http://www.moncefbelyamani.com/how-to-install-xcode-homebrew-git-rvm-ruby-on-mac/#step-3