When I decide to play Nightfall or Factions do I have to start a new character or can I continue using the character I have now?
Also I don't know how, but I had some Mesmer powers as a second skill, then I talked to someone else and he gave me some Monk powers and the Mesmer Powers disappeared. I don't care for these monk powers, is there a way to get the Mesmer ones back? I tried talking to the girl who gave them to me in the first place, but all I have is the option to become a Mesmer for good which I don't want.
Also how do I get more Necromancer skills? Going back to the manual now.
. Want to play not read lol.
You can gain access to all of the expansion areas with any character once you reach a certain point in their "home country" campaign story. My character is from Prophecies, but I've taken her to Factions, Nightfall, and Eye of the North as well. I guess you can technically get yourself to any of them from the beginning, but it requires that you use runners to take your character to one of the hub cities like Lion's Arch or Kaineng Center, and that's expensive (like 5000 platinum I'd wager).
When you're starting out they let you test a small handful of skills from each class for the secondary profession. It's not permanent until you actually accept and become a N/Me, or N/Mo, et cetera. I don't think you can get the temporary sample skills back without making the change permanent, but I wouldn't sweat it. That's still the very beginning of the game.
Getting more skills is half the fun of the game. You can earn them through quest rewards, through purchase from trainers, and through Skill Capture which lets you gain a skill from any enemy boss you kill (bosses are the ones that glow, you probably haven't encountered one yet). There are hundreds and hundreds of skills. For example, the http://wiki.guildwars.com/wiki/List_of_necromancer_skills Add to that all of the skills of your secondary profession, and you've got a huge library to choose from once you actually collect said skills through the game.