To select your character in-game, press E.
In order to attack (PK) another player, hold down the Control button, and double click the user.
To popup your Friends List, press F.
If you are "Driving" a party, the best way to do so it so press and hold down W to move forward constantly without mistakenly clicking on an objest, crashing your party into a wall or just losing the whole lure of Mobs.
The other manual moving keys are - W,A,S,D