Heyo!
To open the console, simply press ENTER once you are on an yland. By typing /cmdlist you can see the complete list of the available commands in the game.
Here is the list
/ban - kick and ban player account from game
/cmdlist - print this list
/demote - demotes a player from admin status
/freecamera - toggles free camera
/kick - kick player account from game
/killme - kills the player
/promote - promotes a player to admin status
/unstuck - unstuck character or vehicle
/w - only those near you will be able to read what you type
Edit 12.2017: just updated the post with the current possible commands.
Take care!
Ane