Activate Snap To Object

If this option is selected, then the mouse position will snap to selected characteristic points of a nearby object when you enter data.

Endpoint

Snaps to vertices and end points  of edges of neighboring objects.

Middlepoint

Snaps to  middle points of edges of neighboring objects.

Intersection

Snaps to intersections of edges of neighboring objects.

Extension

Snaps to extensions of edges of neighboring objects.

Perpendicular

Snaps to perpendiculars to edges of neighboring objects.

Parallel

Snaps to parallels of edges of neighboring objects.

Nearest Point

Snaps to the nearest point of the edge of a neighboring object.

Increment angle

The mouse tracking is limited to whole-numbered multipliers of the selected increment angle, if the Shift key is pressed during  the definition.