[@Pathfinder] Sure, no problem! The canon is notorious for including wave after wave a new details, but the core premis is very simple.

Heroes are summoned from the past by wizards to fight over a wish granting artifact. You can use any Hero from any mythology around the world, (with the exception of a VERY few extreamy powerfull ones, and excepting gods or modern fictional heroes) 

For makeing a Mage, there are more limitations, but it's fairly fiction typical aside from a few things. All in all don't worry about it. PM me if you have any specific questions about world rules, but its fine to be filled in as you go along.