The gaussian tool allows for the terrain to my modeled after the 3D gaussian mathematical function,
A*exp(-u(x,y)2/2*sigma2), where:
A is a height constant
Sigma alters the shape of the curve
To use a tile must be selected, and the enable button must be checked. Note the standard spinner tool "M" means manual edit the number
Note: to speed up preview mode, the changes are not finalized until the tile is unselected. This makes a dramatic difference for computation time however for very large terrains this will a few seconds after finalization and the status of the change (percent) will be displayed in the status area
Note: If there isn't any terrain to click on goto the menu TerrainOptions->GenerateTerrain