Completely new to guild wars, help me!

so i just started playing guild wars today. I actually have had the game for a while but never installed it. First off i have a couple questions:

1. do i need all the expansions?
2. can you see other people from different expansions? cuz i dont see how one person can become an assassin in fations(one i have) and some other person have a eye of the north character.
3. any tips for a noob?

welcome

1. You dont NEED them but its quite fun to have them. And also you can pick them up pretty cheap these days
2, You can see other people, owning more than one game allows you to visit the other games with that character.
BTW they are campaigns aswell.
Prophecies - has 6 core professions
Factions - adds assasin and ritualist
nigthfall - dervish and paragon professions added
depending on where you start depends on what professions your allowed. EOTN on the other hand is a expansion where you must own a previous game. This means you can access the eotn at a certain point in the game. EOTN doesn't have any of its own proffesions.
3.
tips...F10 in game brings up a search option for wiki. The Guild wars wiki tells you everything you need to know. Also just ask some people too, despite there being some rude immature people about, there are also alot of great people.

Dont listen to those who say this game is dying or its all about grind, play it how you want to and just simply have fun.

The game is quite easy to pick up the basics of playing and is quite casual too. There is weekend events to help aswell. This weekend there is special easter items dropping and look forward to the ingame celebration of the 4th birthday,

1. No, you don't. But getting them unlocks more skills, for starters.

2. Yes, you can meet other people from different campaigns. Eye of the North is not a campaign, it's an expansion and your character has to be at least level 10 to access it. If you have more than one campaign, you just have to take the quest to access the rest - e.g if you have a Prophecies character and want to bring him to Factions, just take the quest from Lion's Arch. Looks-wise, however, you're limited. Factions warriors look very different from Nightfall warriors, for example. 'Sins and Rits are Factions only, Dervishes and Paragons NF only.

3. It's probably a good idea to familiarize yourself with your skills ASAP, and unlock more. There's absolutely no need to rush through the game, and I honestly think you're missing out if you do that.

And of course, I mustn't forget: welcome to GW. (:

i just made a ritualist, can i bring him to nightfall or he must stay in factions, only classes that are available in the other one can travel in between?

~ that was horrible grammar, sorry xD

Oh, don't worry - you can bring him over to any campaign you want once you hit Kaineng. NF has Rit armor and Rit skills too, y'know.

You can bring him to Proph, too, but you won't be able to buy skills for your rit there.

Yeah, once you hit a certain part you are able to move your characters between the campaigns whenever ya' want.

If you own nightfall you can take your rit there. There is a quest in Kaineng Center that allows you to travel to Elona.

The other 2 question have been answered...

3.) My Top 5 Tips for New Players

thx for all the help

Familiarizing yourself with GuildWiki can help. It can help answer most questions.

http://guildwars.wikia.com/wiki/Main_Page

Welcome

Factions is more PvP based and the learning curve jumps.

If you need help, whisper me Zodiac Ele.