First and foremost, you should be familiar with GitHub. There are a ton of ways you can contribute without even really knowing Node, Express, and JavaScript all that well.
Ideally, you'll want to get Free Code Camp running locally on your computer, which doesn't require so much understanding of Node/Express as it requires an ability to carefully follow directions (and our project is not unique in this regard).
I wrote a short guide a few days ago about getting started contributing to open source: quora.com/What-is-a-step-by-step-procedure-to-bec…