adding more GW titles

I just started guildwars yesterday and i like it alot but having seen that their are a few packs Proferacys (which i have), Factions, Nightfall and Eye of..... are they add on packs do they in corporate themselves in to the game and they open new areas at higher levels and armours etc or are they seperate and will i make a new char on each ???

They're interlinking, you can travel freely between them on all of your characters on your account (Atleast, if all 4 of the keys are added to the same account)

they all give u access to new content. Factions and nightfall and prophecies are all stand alone games, but eye of the north is an expansion, and it requires one of those 3. u can add all games to your acount and use the same character on all 3 games and the expansion. each game gives u a whole new map to play through, and EoTN gives u access to the top half and some other areas of prophecies.
hope that helps