Your first step is to create the directory where you will work - its where both code and parts live. This assumes you are using git but you could in theory just download them. If you do use git, you can fork and submit pull requests for subparts and more. We don't cover git here, its assumed you know how to use it.
Clone https://github.com/adafruit/eagle2fritzing into that directory
Clone https://github.com/fritzing/fritzing-app into the same directory