Understanding Einstein
The Special Theory of Relativity

I recommend taking the course : Understanding Einstein: The Special Theory of Relativity. If you don't want to enroll, there are videos available online that you can download and watch. PM me if you want a link.

Prof. Larry Lagerstrom's special theory of relativity course. Here's the link

As you go faster, time slows down. This really doesn’t do anything until you get to VERY high speeds like 10% of the speed of light. Graphically, once you go past the speed of light you’re technically going backwards in time. The problem is that at the speed of light or past it the equations used to calculate this change in time and the energy needed to get to that speed break down, so it is literally impossible to reach the speeds needed for time travel

Edit: here’s a free pretty simple 8 week course on the subject if you’re interested in the subject

There is a terrific short course on Coursera from Stanford that explains all of this in a really basic way. Check out https://www.coursera.org/learn/einstein-relativity

This is a good course even for newcomers to the ideas of relativity.

I haven't read any books about the subject to be honest, but I've taken this course which will make you understand the theory without using any advanced maths, and I highly recommend it https://www.coursera.org/learn/einstein-relativity

One final comment on this: I learned special relativity in school long, long ago. But I found that it really helped refresh my memory and build my intuition and understanding to take a Coursera course on this subject.

I'm pretty sure it was this one. He spends a lot of time drilling into you how to think of events from the standpoint of different observers, and to show how everything works out self-consistently with the Lorentz transformation.

He also does a really good job introducing and explaining Minkowski diagrams, which are perhaps the best way of all to understand the relationships between different observers descriptions of events. In particular, the twin paradox just jumps right out from the Minkowski diagram.

If you're looking to actually understand why time slows down the faster you move through it. Then I highly recommend watching this video series. https://www.youtube.com/playlist?list=PLoaVOjvkzQtyjhV55wZcdicAz5KexgKvm

Now, if you want to add more depth to your understanding of special relativity. Then, give this free special relativity course a go, https://www.coursera.org/learn/einstein-relativity

Learning special Relativity, surprisingly, doesn't even demand a high knowledge of math. You just need to know some basic algebra and you're golde. The course also features a math section that a 6th grader can understand.

Keep in mind though, special Relativity only helps you understand why time slows down the faster you move through space. It doesn't explain gravity's influence on time.

Check out Physics courses on Coursera. Same with math courses. They vary on difficulty but usually the ones tagged as Beginner will give you a review lesson. I've only taken one related to astronomy, here [Special theory of relativity], and it wasn't that bad with basic math you probably know. Pretty much any Joe can jump into beginner courses—intermediate might be beneficial but haven't tried any.

A lot of them have extra homework you can do that is more math-centric. They're probably worth doing if you want the practice.

There is no harm in enrolling for a class and just browsing the course to see the assignments either.

Class central seems to be a hub when looking for online classes. Lectures online are good too. Unless you find a certain field of interest, beginner courses are probably what you would expect from first year college, if that. Just really watered down.