Remember that repetition is the heart of learning. If you want someone to understand Relativity to the same degree Einstein understood it, you don't start with the math. You start with an analogy (which obviously doesn't match reality). Once they understand that you can add more analogies (maybe about just parts of Relativity). Eventually you build up from parts to the whole and from broad analogies to specific details. Over the years this is happening you will be gradually introducing shortcuts and jargon. But, only a master of the subject can explain a complex topic in simple terms. I can't tell you how many times my children have asked me a question about something I thought I knew, but once I started trying to explain it in terms they would understand I realized that I really didn't understand what I thought I understood. But if I spent a little bit of time reading up on the subject again then I found that I could explain it to them in such a way that they could correctly explain it back to me.