when i buy the packs

ok so i read the wiki and the stickys and i am still not sure about something ok so if i install all the xpansion packs factions,nightfall,propehcies,etc and can i combine them all like if i play in prophecies i can still make a assasian in prohpechies cuz i have factions?i dont get it.

No, you can't create an assassin or ritualist outside of Factions, however you can bring your assassin from Factions to Prophecies/Nightfall/Eye of the North once you reach a certain point; Kaineng in this example.

You can only create Dervish and Paragon in Nightfall. You can create any of the 6 core professions in any campaign.

Factions and Nightfall are not expansions, they are chapters. The only expansion is Eye of the North.

As long as you have every campaign or expansion on ONE account (very important!), you can play them with all your characters.

But 4 of the 10 professions can only be created in a certain campaign:
* factions: assassin and ritualist
* nightfall: paragon and dervish

You cant create characters in eye of the north (expansion)...