Your kuksa is probably empty so you can't do anything with it. Left click on the kuksa, then when it gets on your mouse pointer right click on a water source such as a well or a river. If you click on the well wait a few seconds for the graphic to show the handle going around. Then left click on an empty square in your inventory again to put the full kuksa back.
After this when you right click on it you will get the options drink and empty.
Thanks a lot. Im really having a hard time with this game. It feels like it should have a interface more alike with TIBIA. I still dont know how to open the console though
if you're using pacho's client (and you should), the console is accessed by the ` key
on the default client there are some console commands that are used by typing : and the command into the main game window, mostly camera commands like :cam fixed, :cam cake, :cam kingsquest. there are also some commands for controlling sound and background music but i don't recall them offhand. you can also type :lo to log out. the : commands also work in pacho's client.