I believe an expanded answer is needed.
However, you seem to be in the so called "pre-searing" part of the game. That part of the game is essentially just a large tutorial during which you familiarize yourself with the game and acquire your secondary class.
The party size is determined only by the area in which the party is being formed. The player level has no effect on this. As such, the area you are in is limited to parties of two people. The rest of the game areas allow parties of at least 4 people, so the second you finish pre-searing, you'll be able to play with your friends.
As for your secondary profession, you can acquire it at lvl 1, essentially. The whole pre-searing is intended to introduce you to the secondary classes by temporarily "giving" you a secondary class, so you can try out all of them. However, you can simply accept the first secondary class you are offered, and have it almost instantly (all it would take would be a walk to the class giver and performing his/her quest). A mesmer secondary could be acquired in 5 minutes, as the trainer is right outside the city gates

.
However, for a new player, I'd suggest thoroughly playing through presearing - you get your basic skill set from the quests there. Also, once you leave presearing, you'll never be able to return...