It all depends upon the time you have. I was once in a position to fix an issue in an open source project that used Django. I had very little knowledge of Python and 0 experience in Django before. So I told myself this is not rocket science and I am not going to give up until I figure this out and started working on the issue. To my wonder, I was able to figure it out by evening. So I would recommend you to get an issue to work and jump right into the codebase. if you don't know which files to modify use the grep command. Go through documentation, tutorials and all only when required. Remember this is not rocket science. Learn as much as you can from the existing codebase.