I would highly recommend reading this collection of essays compiled into a book titled "Einstein's Theories of Relativity and Gravitation" There was a competition for anyone to explain Einstein's work for the layman and a lot of people wrote essays to win the $5000 prize, this book has the top essays that were chosen and really helped me get a grip on the idea of relativity.

https://www.google.com/books/edition/Einstein_s_Theories_of_...