Understanding spacetime physics isn't easy, but understanding the basic theories that scientists now believe paint the most realistic picture isn't that hard to comprehend. It just takes the curiosity and the patience to focus, open your mind, and consider. But first you are going to need a good book, one which is illustrated. Also a physics reference book which can walk you through all of Einstein's theories along with others who have added new concepts to the sciences of space / time physics.
Luckily, I own such a book, one which was published in 1966. You may think that is too old, and that we've learned a lot since then. And yes, yes we have, but the fundamentals are relatively the same, especially when it comes to "relativity" or the theory of. Now then, the book I'd like to recommend to you is:
"Spacetime Physics" by Edwin F. Taylor and John Archibald Wheeler, WH Freeman Company Publishers, San Francisco, CA, (1966), 208 pages, Library of Congress Card Catalog Number 65-13566.
Both of the authors are / were physicists, one from MIT, and the other from Princeton. The book starts out with a discussion on the geometry of spacetime, and all the theories, rules, principles, and unknowns which go along with that. Then it gets right into momentum and energy; How they relate to mass, and the expanding universe – and there is a rare find – an absolutely fascinating dialogue on the concept of mass, light, and the arguments of spacetime physics, at least at the time in 1966. Some of which has been resolved but not all the points of view are agreed upon – humans still have more to learn.
If you've been stuck on anything with relation to Einstein's theories or are hung up on curved spacetime, gravity warping, or the differences in force, mass, or the principles of relativity – you will be quite pleased to have most all of your questions answered. Those which cannot be answered or at least could not be answered back in 1966 are not there, but you will have a great understanding up until that point, and be able to ask the right questions to continue your personal research online.
My favorite points in the book were the reasoning of the various paradoxes of time, space, energy, motion, light, and so on. It's just a really fun place to think, and this book will take your mind around the universe and back, as well as through time and back again, and thus, I come to you with this excellent book recommendation. So, please consider all this and think on it.