The same way I know about any type of history that happened more than 23 years ago. History books, documentaries, the internet. It's all fascinating stuff. You were not alive in 1776, but can you tell me some of the details of the Revolutionary War and the feelings and mindset of the colonies? I bet you can...
I love geeky culture like Star Wars and Back to the Future, and yes TRON. I know how they were made and what the general consensus was when they came out. Computer graphics were not heavily used in film before TRON. They may not have been the best, but they served as inspiration for lots of filmmakers after them.
And before anyone says anything, no I did not think Inception was confusing.