How does a video game expansion pack work as in does it load into the main game or is it separate

Expansion Packs You have it right. Expansion packs in a nutshell are "extras". For example, the game Diablo II primary game comes with 4 acts. There in fact 5 acts. If you want to play the 5th act you have to buy the expansion pack, install it, and everything from the previous game such as your stats and items and spells will be carried over. You then simply play off the expansion pack CD. Other games like roller coaster tycoon come with certain types of rides but other types are exclusive to expansion packs. You then buy expansion packs and install them and then either use the expansion pack CD or the regular CD to play off of, or you can simply install everything to the hard drive. Expansion packs are usually less expensive than their full version counterparts. Some games like everquest release tons of expansion packs. These are usually open ended types of RPGs like Everquest and Baldur's Gate. Make sure you have a good size hard drive (100+ GB should do it)if you run everything from the hard drive.