Civ2
The original release, version 1.00 up to 2.42 (a freely available patch, available
HERE, among other places).
CiC
CivilizationII Scenarios: Conflicts in Civilization (version 2.62, there´s also a small update to this version
HERE, for instance)
The first add-on, including the first version of an events language as well as several scenarios.
FW
CivilizationII Fantastic Worlds (version 2.78)
The second add-on, including an upgraded events language, more scenarios and scenario editing tools.
MGE (dunno which version, higher than 2.78 obviously, the latest patches, again, are available
HERE)
CivilizationII Multiplayer Gold Edition
A stand-alone version adding multiplayer, includes the previous two add-ons. Also known as UCC (
CivilizationII: Ultimate Classic Collection). MGE is often used when referring to any multiplayer version (I believe), including the multiplayer add-on, which requires a previous version of Civ2, in contrast with MGE/UCC.
ToT
CivilizationII: Test of Time
A new Civ2, based on the same game-engine, but with a different interface and different graphics. Also adds new variants of the game, such as a fantasy game, a science-fictional game and the possibility of continuing to play on Alpha Centauri. This version is not compatible with any of the previous versions.
To see which version you have, go to File > Game Options and check the title bar of that window.
Did that clear everything up?