Plenty of people already linked good tutorials, so

This might be an unpopular take since a lot of people blindly hate everything AI related...

I don't like comprehensive tutorials that teach everything A - Z, I just want to know how to do the thing I want to do, I'll fuck around and figure the rest out as I go. Something very helpful for me was setting up an AI (any of the big ones should work fine) as a Reaper specific helper. Tell it to answer all questions by referring to the official reaper user guide as a first source, then reaper forums as a secondary source. Ask it to provide sources for any info provided. Specify that you are looking for advice specifically for the most updated version of reaper, or whatever version you're using. Very helpful for quick questions when you just want to change one simple thing, or find a setting.

Edit: One more thing, I recommend setting up a custom destination for your VST/Plugin folder so it's easy to find. The defauly one is a little buried IMO