It's really easy to be intimidated by terminology and process when considering contributing to open source projects, regardless of your experience coding. There are some small steps you can take to get you familiar with a project immediately using github.
The first step I suggest (outside obviously reading project documentation) is focusing just on conversation and not code. When you sign up for a free account, you can browse projects. At the top right of the project page, you will see a menu with "Watching" state. Simply turn on Watching and keep an eye on posts.
The next step I would suggest is to get familiar with issues that have already been posted in the project. On the right side of the project page, you will see issues. Open them up and start reading any that are relevant to your skillset.
You will now receive updates based on project conversations and improvements, and any Issues that you receive replies to.
The context and conversations in these updates are really helpful to understanding how it all works, and will grow some confidence in code contribution.