how do you make the first ground so you can lay out objects on it?
Create → Game Object → Cube? You may want to go throught the tutorials man, this ain’t Little Big Planet.
Have fun with Unity! 
As a playground to start with I would just make a new GameObject>Cube. Then change its sizes to 100, 1, 100.
Else you can make a new terrain.
I don’t have unity on this PC, so can’t look up the exact names…