Who can teach me how to abuse the frame data because I read it and still find it to be foreign.
Like what exactly, punishes and stuff? That's something you need to feel more then know, especially in Smash because you're almost never going to be face-to-face like in traditional fighting games.
Pit's ground punishes range from f5 to f10 (f20 with an Arm and the second hit of D/Fsmash) so it's not like you need to be very picky, besides Usmash for obvious reasons. To me if you're sticking to the ground it's using the move with the most damage/potential damage/killing potential then anything, so mostly grabs and dash grabs.
If you're going for a flashier air combo though, that's tricky because Pit's aerials typically come out slower, his air speed is poor, and jumpsquat is always an extra 5 frames of start-up. The fastest Pit can put out an aerial hitbox from the ground is f9, Nair. (Fastest anybody can is f8 besides Mac's f2 Nair I think.) Dair would be f15 in the back, f16 up front.