Hi Goodgey, seems perhaps you are either A) A young whipper snapper B) Really over thinking this C) Not that interested in any nicheness or competitive elements of MTBing and just enjoy being on the bike. I know people who have taken the courses who instruct or guide in other sports and have good leadership and navigation skills and can ride a bike but would not have the knowledge of people on the forums.
My advice is to go to the British Cycling website as they have definitions of all racing disciplines (Cross Country).
Google single speed bikes and then single speed events and it will all make sense.Try and talk to some other riders (older/younger) when you can and read some mags. Then you keep up with innovations, trends, trails and events.
Hope that helps, all the best.