interact with stuff outside the house, everything should be clear once you find the right object.
but if you want a more straightforward answer, there's a garden gnome by the fence in the northeast section of the area, pretty close to where lisa's car is parked. interact with the garden gnome and you'll find a patch of dirt underneath it. to dig up the patch of dirt, you can find a shovel by the road pretty close to the mailbox and a few trees. pick up the shovel and interact with the patch of dirt, then you'll get a key to the house.