John’s RC Sailing Rules and Tactics
There is a very good explanation of racing rules here with pictures. It’s well worth a look and is one of my go-to places when I’m unsure.
Bryan Willis Racing Rules
There is a very good pocket sized flip book by Bryan Willis available from all good booksellers as well as eBook Its Called Racing Rules 2017-2020
We are all about sailing and that requires an understanding of some simple rules. The MYA UK has a very good simplified booklet which may be downloaded here for FREE.