Are there any online classes or similar stuff that teach how to be a ‘DM’ in ‘D&D’?

Are there any online classes or similar stuff that teach how to be a ‘Dungeon Master’ in ‘Dungeons and Dragons’? If not then is there a textbook that can help or maybe some tutors to hire?
Answers

oikoσ

TSR Games has published numerous books on D&D games, including Dungeon Masters Guide, by Gary Gygax. You don't get more authentic than that. The book came out in 1979. TSR is (or was) at P.O.Box 756, in Lake Geneva WI 53147.