Quests are side missions that you can do to earn extra cash and loads of EP (Experience Points). To do one of these missions, simply click the quests tab at the top of your game window. New quests are automatically accepted.
Stations are places where you can trade, repair your ship, or just relax and chat for a while. Every station has it's own safe zone, but note that Scion stations have no safe zone for Jafnhars and vice versa.
Fish are NPCs that roam the water, some are aggressive, and some only shoot when shot at. Fish get more powerful as you go up, so the level of your ammo matters.
Throughout the water you will see other players, these players can attack you at will and vice versa. You have newbie protection until level 6 though, but after that you're pretty much fair game to everyone. PvP combat can range from a simple 1 vs 1 to a full out clan war.
You can group with other players, by pressing "G". This will bring up a group window, where you can invite someone to join a group. When someone invites you to join a group, usually the group window will come up automatically. When it does, simply click the check mark by the person's name to enter their group. When in a group, you will share all EP and money 50/50 between you, unless there are more than 2 people in the group.