Can't find my way

[Nice]

Hey, I'm new here I need some help. I've just begun playing, found a letter saying I must kill Alexander, passed through a red door then got stuck. I cannot find my way. There is no door, just a hole on the ceiling. I tried to put the boxes one on top of the other and climb on it but couldn't succeed. Help, please?

If i remember correctly there should be a lever on the wall which you need to push down. A secret entrance will be revealed after