Along with a description of the Academy, in this article by Josh Gentry you'll find new bonds and flaws, new feats such as Imperial Pyromancy and Occult Informant, outlines of significant NPCs, rumours and plot hooks, random faction conspiracies, and the Imperial Pyromancer stat block. ...
In my games, you can train a commoner into a guard, and a guard to a soldier, and a soldier to a knight, and so on, but it isn't easy. It can take years. That isn't canon to 5e, it just makes sense that you're not stuck as what you're born as....