Well first off, if you're using the side-B / down-B thread, don't pay any attention to the names/pictures, since I changed them for April Fools day.
I kind of figured that there weren't really going to be any new Sonic mains so I haven't really bothered to fix it up rofl.
Sonic is terrible to play unless you have a grip on pressuring people - like know how to space yourself when they're on the edge, chase people when they're trying to land/recover, have a feel for when people like to airdodge, spotdodge, roll, or attack in defense.
I'd strongly suggest that after you get a good grip on those, then come back and start working your B-move game lol.
As for AT's, there's spinshot, which you can look around (there's an rFAQ [really frequently asked questions] thread) for input help.
The most prominent "AT's" are:
Spin Cancels
side-B shield cancels on the ground while it's charging.
down-B shield cancels if you release it in midair and hold shield as you land.
Spin Charge is the official name for down-B, so we call aerial down-B's ASC.
Foxtrot/Dashdance/Dashdance pivoting
Foxtrotting is just tapping forward at a steady rhythm - if you do it right, Sonic will restart his run each time you tap it.
Brawl Dashdance is quickly doing a forward-back-forward-back... etc motion so that your character starts turning around in place.
You can use Dashdance to turn around during a foxtrot, and that usage is what we call Dashdance pivoting/ DDP.
Again, they're all pretty useless/just for flashiness unless you have a grip on pressuring/reading people.
x.x;