When I went to the bridge,he droped me into the water,then I ran to the tunnels and came to the romm where is flyng a lot of blue heads(maybe ist's a spell name..don't remember),and there is a key on the ?table?,but I can't get him because he's too far,is there some trick,or I'm so stupid because can't take a key

Just CLIMB up onto the table and snag it. You might have to jump first, then climb the rest of the way up.