Beginner here

I recently (yesterday) decided to buy and try Guild Wars. I've been playing Everquest for the last 10 years and finally decided to try something new.

After I install the game and create my character I'm faced with a selection:
"Prophecies" Faction "Nightfall", which one of the three should I start with or does it matter? I decided to start out with a ranger. I tried Prophecies, then I made a Necromancer and tried Nightfall. They both start me in different areas, so I'm wondering there a sequence I should choose them in, can you play all 3 on the same character once you finish one, or can you finish them?

The campaign you start in does matter. As you've seen, they start on different continents. Once you reach the port cities (Lion's Arch in Prophecies, Kaineng Center in Factions, and Kamadan in Nightfall) you can move to the other continents and play through the other content. You won't be able to do the beginner areas on foreign characters though (so the Ascalon stuff would not be available for a Nightfall character). Other than than, it affects how your character looks (though you can change your looks if you buy credits through the in game store) and the professions available (Assassin and Ritualist are Factions-only and Dervish and Paragon are Nightfall-only). Prophecies is the easiest campaign as it has the slowest learning curve. Factions came out a year later and then Nightfall 6 months after that. The later campaigns sometimes make reference to things that happen in the previous campaigns so I recommend completing them in the order of release (the difficulty is more appropriate that way as well). There is nothing stopping you from making multiple characters in different campaigns to see which you prefer though.

Thank you for the reply, that was quite helpful in choosing a starting point. Now if I could just make up my mind on a character .

Thanks again.