So now we have a house with no doors and no windows. Let's split one of these brushes and provide an entrance to our lovely home. The Clipping Tool will clip (cut) parts of a brush off, or split a brush into two sections; the icon resembles a cube with one of the edges cut or chamfered off. You can also press Shift + X to select the Clipping Tool. You need to select the brush you want to clip before you select the Clipping Tool because you cannot select an object with the Clipping Tool selected! Select one of the long walls in our house and then select the Clipping tool. Drag a vertical line in the middle of the brush where you want it to be split. The clip line is defined by two white handles connected by a light blue line. The clip line extends along the entire selection so it's not necessary to perfectly align the handles with the edges of an object, but it is good practice because it will help prevent off-grid vertices.

Notice that one half of the brush is red and the...