It looks as if your models are just hanging in the air and you have no lighting in your level at all.

Dont use a model for a castle, and dont put your level inside some brick block. Use a sky instead. Put your models on a ground plate, and if its an outdoor level use sun light and ambient instead of a light source.

Have a look at other peoples levels, I think there are enough on AU to get an idea how a level is built. And sure, why don't you read the tutorial as a start?