When you are prompted for a location in a drawing, you can use one of several methods to specify the coordinates.
Use the mouse to select an AutoCAD Civil 3D point in the active drawing.
Enter X, Y (and Z, if prompted) coordinates at the command line, separated by a comma. Alternatively, click a location in the drawing. You can use AutoCAD Object Snaps to select a point accurately.
Some of the Civil transparent commands calculate point locations from angles, distances, and drawing geometry.
You can send drawing coordinate information to the command line based on cursor location and a specified surface.