Missions and quests

how can you tell the difference between a mission and a quest. Can you do missions with a friend? If your friend already copmleted the mission can he still go back and do it with you?

A quest is in your log, usually not as essential, and has specific rewards listed. A mission starts a specific mission outpost, progress the game storyline, and leave you at a new area.

In addition, missions can be done multiple times, but you're only rewarded once. Also, missions have to be done all at one time, you can't do half of it, quit, and then do the other half. Third, missions take you to places on the map that you can't get to if you don't do the mission. Fourth, missions always give 1,000xp and 1 skill point, and the bonuses always give 1,000xp. Some of them give additional rewards but I'm not sure what the deal is with that. All I know about that is that one time I noticed that on a mission or bonus, not sure which, it said something about getting 3 platinum split between our group.