Isn't that described in the manual? You may get a faster response asking in the German D2:ED forum.
The skill system has changed from the previous 2 games, but if the interface is remotely similar, when you select a skill in the skill tree (or list), there should be a description of the next level (effect and level requirement, if any), and some kind of plus sign or checkmark button to assign any free skill points to the selected skill.
Did you try attacking locked containers? In DD you could smash open locked barrels or vases with a melee attack (though not chests). That was no longer the case in BD, but they may have brought it back.
There is a quest log. Try the hitting the 'q' key, or check the game options to see if a quest log is listed in the assigned hotkeys. In the previous games if you opened the map there were icons there to switch to the quest log, etc...
Welcome to the forum.
