The advice so far in this thread is great, but I'll add one thing I did back in my former manager life, which was to have a scheduled time block each week of a

The advice so far in this thread is great, but I'll add one thing I did back in my former manager life, which was to have a scheduled time block each week of a few hours for general Q&A. Each week I'd have them pick a topic or area they want to learn more about, and I'd go in front of a whiteboard and explain things to them in as much depth as they wanted. We'd go over the codebase, how it fits in with the rest of the organization, historical reasons why things work they way they do... or even just help getting their dev environment set up, reviewing code, etc. Of course, everything was already pretty well documented and explained in other places, but nothing beats actual 1:1 time to help with any confusion they may have. It helps build confidence because they know that time is a safe space to ask any question, no matter how "dumb", and that it's all for their benefit. It's also beneficial for there to be multiple hours of time set aside, so that we could actually dive deep and not just leave things as an exercise for later. I was told this was their favorite part of the early months on the job, because it helped build confidence and skill more than any other single thing.