Well, yes, it's a ton of information to assimilate, but you need to start doing it. Just on the steam, every wheel notation has a "name", sometimes more than one, associated with it. Does it do you any good to know that you have a "Consolidation" of you don't know what that means? I'll help you on that one -- it's a steam locomotive with a wheel configuration of 2-8-0 -- two non-powered wheels (one axle) under the pilot of the locomotive, 8 drivers (powered wheels) and 0 trailing (unpowered wheels). The rest of the steam works the same way.
Likewise, a lot of the diesels look similar at first glance. You need to start getting a feel for what an ALCO diesel looks like. How about a GE model? What is it that makes it one or the other? Otherwise, just run your GN diesel. Does it really matter if it's a GP-18 or a GP-25? GP and SD models are made by EMD.