You can view all available plugins for Oh My Bash under the Plugins directory.
Once you spot a plugin (or several) that you'd like to use with Oh My Bash, you'll need to enable them in the .bashrc file. You'll find the bashrc file in your $HOME directory. Open it with your favorite text editor and you'll see a spot to list all the plugins you want to load.
For example, this line might begin to look like this:
plugins=(git bundler osx rake ruby)