The simplest heightmap tool is the Elevation tool. It is used to simply raise or lower an area within your selection one layer at a time. For the time being the brush options only let you configure a cylindrical shape from which the Radius and the Height of the brush can be configured. These are pretty self explanatory where the height setting affects the y range in which the blocks are affected and the radius is the size of the heightmap.
The Sharpness setting lets you change the behaviour of the aforementioned curvature and falloff. Increasing the sharpness makes the edges sharper/more flat.
Then there are the raise and lower modes. This affects whether the brush will add or remove blocks from the world.