To switch snapping on or off press
The snapping feature has a numerical parameter - the divisor, which shows how many segments the edge/line will be divided into, so the cursor could snap to the end-points of that segments. This divisor is shown as a small number in the corner of the snapping icon. You can adjust it using
Scroll Wheel. The possible range is from 0 to 8:
0 means that the edge won't be divided into segments and the cursor won't snap to any points. It will snap to the edge itself only.
1 means that the edge will consist only of one segment, so the cursor will be able to snap to the edge's end-points as well as to the edge itself.
4 means that the edge will be divided into 4 equal segments, so the cursor could snap to the edge's end-points or to 3 points in-between equally distributed along the edge.