Well, depending on your preferred format there's a great book called A Brief History of Time - https://en.wikipedia.org/wiki/A_Brief_History_of_Time , or lots of videos about it at https://www.youtube.com/results?search_query=time+dilation

More broadly, the series Cosmos with Carl Sagan was excellent, and is worth a view. The bit about time dilation is at https://www.youtube.com/watch?v=kWgEzxi_A0w . The more recent one with Neil Degrasse Tyson is also good (but while I enjoy both, I think I prefer the older one)