Its different for most of the characters. Some share the same combo system such as Ultimate Gohan, Cooler (Including Metal) and Frieza (Including Mecha). What differentiates the air combos from the grounds is just that. Ones in the air and the other is on the ground. The air excludes your jumping combo.
Other than that everything is the same depending on the character. By the way you should check out my new nail fight you'll love it.
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You really just have to experiment really. Just test all the smash attacks and their follow-ups (when you do a smash attack and press x,y or be straight after to make a quick string) also, knowing the air combo will help with Raging Soul combos as a plus. The air combo is the last thing you should do in a Raging Soul combo to perform a ping-pong move.
Their just basically smash attacks with follow-ups. I'll give you an example, Scouter Vegeta can do Smash Attack 3 which is X > X > X > Y from there if you press Y he'll do a follow-up Smash Attack 2 (the ki push move) then if you press Y again he'll do a follow-up into the air combo. I don't think it necessarily needs two follow ups, Goku can do smash attack: low and follow-up with Y to go straight into the air combo. You really just have to experiment unless someones posted the follow-ups online.