Accepted an offer, what now?

I notified the department and received an email from my PI that he’s excited to have me etc. but what happens now? That was a few days ago and I haven’t heard anything else. I know a few things I have to do on my end document wise (official transcripts etc.) but outside of that I don’t really know what is next. I don’t have a university email or anything yet and I know fall registration for courses opens soon. It just feels silly I did so much research on PhD applications and the PhD itself but have zero knowledge of this transition phase.