I think the original Civ2 is sometimes called "Classic" or "vanilla" or "version 2.42" though there may be some slight differences.
Next (AFAIK) came Fantastic Worlds (FW), which allowed users to make scenarios with event files etc. I don't have it, but one post said the diplomacy doesn't work well (the same as MGE ?) and I think it is less common.
Then the Gold Edition (or MGE) which allowed multi-player games, and maybe slightly better scenario support (not sure). I like the interface better than Classic, and recommend this version if you plan to play scenarios, MP or PBEM (email). The AI is more hostile though, so I often use Classic in GOTMs.
I guess ToT (Test of Time) came later, and it may be even better for scenarios. But I don't have it, and get the feeling it is less popular than Classic or MGE.
IMO the first three are pretty similar. You can open saves made by Classic if you have MGE, but not vice versa. AFAIK ToT is not compatible with either one (not sure about FW). I have probably left something out, but I think there is a complete history in the Great Library (Index 1) at Apolyton if you want to know more.
Conquest Dude: What did you want to know? If you have the MGE manual, it describes scenarios pretty well. I don't know of a separate product called "Civ2 Scenarios", though. You can DL them all for free AFAIK.