The main editing area shows the terrain, editing markers, track and NL area boundry. Water, markers, track and area boundry can be toggled on and off. The terrain detail underlay texture can also be toggled on and off. To edit terrain, use the mouse to point and left-click the markers on the terrain. When a marker is selected, it will change to Red in color. These are Primary markers. Also, an area around the marker will be changed to Yellow in color. These yellow markers are Secondary markers. The secondary markers indicate the area that will be effected by Area tools and by Auto-Smooth. You may notice at the edge of the yellow markers are green markers. These markers simply indicate the end of the effect area.

To clear selected markers, you can either use the Clear All Markers option from the Tools menu, the Toolbar or by pressing the Space Bar on your keyboard. If you just want to unselect certain markers, hold the Delete key and left-click the marker you want to unselect. Remember that only Primary markers are Selected or Unselected. Secondary markers are only for visual refrence of the Effect Area.

To modify the terrain, once you have at least 1 marker selected, hold the CTRL key and left-click with your mouse. Holding the CTRL key and the Left mouse button, move your mouse up or down to raise or lower terrain. Optionally, you can hold the SHIFT key instead of the CTRL key to move the terrain fast. Or you can hold the SHIFT and CTRL key to move the terrain slowly.
CTRL + Left-Mouse = Move terrain at normal speed.
SHIFT + Left-Mouse = Move terrain at fast speed.
CTRL + SHIFT + Left-Mouse = Move terrain at slow speed.

Alternately, if your mouse has a Mouse-Wheel you can use it to modify the terrain.
Mouse-Wheel = Move terrain at normal speed.
SHIFT + Mouse-Wheel = Move terrain at fast speed.
CTRL + Mouse-Wheel = Move terrain at slow speed.

Additionally, you can move the camera with the W, S, A and D keys.
W = Move forward
S = Move backward
A = Side step left
D = Side step right
+SHIFT = Move fast
+CTRL = Move slow
Use the Right-Mouse Button to toggle between Editing Mode and Camera Mode. In camera mode, use the Left-Mouse Button to move forward. Moving the mouse around will Look in the direction the mouse is moved.

For a full list of the controls, see the Controls page.