You actually need help playing as MK? That's unusual (for real).
I'll give you a really short guide.
Fair/bair is your spacing tool. You should dash up to where fair/bair reaches and...fair/bair lol
Dair camping is when you dair from a shorthop or full hop fair/dair, and do from 1 to 5 more dairs while airjumping (I do 2 more), then tornado. Move your tornado away if it isn't safe to keep it there. So the technique goes like this: fair/dair, dair(s), nado.
So dair or fair/bair are your two approaches and they work excellent (walking dtilt is nice too, you can't just do two things)
You can perform aerials on airborne opponents. Fair/bair work, but if they're above you, airjumping into uair, uair, fair/bair/upB works nice (I personally don't like the last hit to be an upB since I save it for KOs).
Falling opponents trying to fall back onto the stage are easy targets for a tornado. Catch them with the sides of the nado, not with your face.
Opponents that are trying to recover...aerial them, upB them, edgehog, wait for them, whatever, you'll get used to it. As for your recovery, glide, tornado and drill rush work.
dtilt to fair is safer, but dtilt to dashgrab is cool, and it works if you tripped your opponent. Grabbing someone and getting them to the edge means grab release/fthrow to EDGEGUARD TIME!! Grab release to dtilt/offstage dair to more aerials or a shuttle loop works excelent.
If I'm missing anything, you'll figure it out.