Before you do anything else, you'll need to update your operating system to OS X Yosemite (10.10). This free update is necessary to ensure that all of the required tools install correctly.
To install the update, visit the following link and install the update using the app store: https://itunes.apple.com/us/app/os-x-yosemite/id915041082?mt=12
Once the update finishes you're ready for the next step!