I've converted GHZ act 1 into Sonic and Knuckles Collection format, now how exactly do i get the level in the game?
Well... You'd have to find the location of the data for the level you want to replace in the SONIC3K.EXE file (probably requires looking through the "disassembly" on Sonic Retro's GitHub in IDA Pro) and use a hex editor to paste it in. It's much easier to just edit the Megadrive version.
Using LevelConvertor to port levels into S3K is very hard to do, as if their are too few or two many blocks, the game crashes while loading the level. While their are ways to circumnavigate this, they're really annoying and aren't suited for a beginner. Personally, I think you should start with Sonic 2. I've made several hacks, and know basic ASM, but still don't really mess with S3K; it's a vast, complicated game, and the available disassembly for it isn't very self explanatory.
Pacguy, don't misread him, he's targeting the Sonic & Knuckles Collection for the PC, apparently. Which is something I actually admire, shame to read that it's so hard.
I can't imagine being any easier then Mega Drive S3K (If anything, it's far, far harder). My point still stands.
I have considered making a S&KC Mod Loader in the vein of the SADX Mod Loader, that could make level edits (or any edits really) simpler. Maybe one day I'll actually do it.
Actually, that sounds like it would be rather nice! I've heard it has a lot of neat features that put it a step above the original S3K, which would make modding it a little more appealing. Of course a Genesis back port would really make my day, but that's probably less likely...