Sculpting, or landscaping, is not a major part of the gameplay as when you place a building the land will auto-adjust to allow your building to be placed. Occasionally though, the land may be adjusted in a way that may prevent you from draw roads and paths where you'd like to, or you may just want to visually tidy up after you've destroyed some buildings.

To sculpt the land, use the sculpt tool in the bottom right of the screen.