Hey, I know how it is to start mugen and not have much of an idea as to where to start. So I recommend you watching this video on youtube from the websites channel called Ultimate MUGEN Beginner's Guide (How to add characters, stages, and more). It covers all the things that a beginner wants to know like what version you should download, how to download characters, how to get new stages or screen packs and even how to add music onto your game. I hope this information helps you, good luck!