"I spend the summer at home."
Translation:Jag tillbringar sommaren hemma.
Late answer but I find it easiest to think of hemma and hem as having inbuilt preopositions ie. hemma as meaning at home, and hem meaning to home. Obviously these are not literal translations and there are probably cases where this doesn't work, but it helps me remember that no preposition is needed in sentences like this one. Hopefully it helps someone else too?