There are two EQ games, one being the original, EQ, and the other EQ2. If you havent played before, I would highly suggest starting with EQ2 instead of 1 as Prometeus pointed out, the community on 1 has been around for so long that most players are geared to the high end raiding and there wont be as many newer players to start out with. EQ2 has been around for 2 years, but there has been a huge influx of new players with the recent expansion Echoes of Faydwer, that you will have little to no problem at all finding new players to meet and group up with.
If you're asking about expansions, which are additions to the games, for EQ2 I would just go buy the Echoes of Faydwer, which will include the game and all the previous expansions for EQ2 for a reasonable price.
Hope that helps