I would start with Nodeschool.io, there is a lot of information and good things to learn.
You should start with the core ones, and if any of the electives are interesting follow through with them. I can guide you as far as what to get into after the core ones if you’d like, but definitely start with the core ones.
I don’t see any specific to websockets, but tbh that is only a small part of using node, but it is a useful part. You would need to get used to everything else otherwise you might get overwhelmed.