These tools restricts cursor movement to specified increments. To select this just go to
Menu Settings-> Snaps-> ....
You can also select snap tools from Snap toolbar too. This is as follows.
There various snap tools as follows
Ortho Snap :- To restrict the drawing a line horizontally or vertically this snap is used.
Snap Grid :- It makes snap grid on or off.
Point Snap :- To select the nearest point this snap is used. How To?
Endpoint Snap :- To select the end point of any entity this snap is used. How To?
Mid point Snap :- To select the midpoint of any entity this snap is used. How To?
Centre Snap :- To select the centre point of any closed entity like circle, rectangle or ellipse this snap is used. How To?
Perpendicular Snap:- To snap to the perpendicular point of another entity this snap is used. How To?
Intersection Snap :- Use the Intersection snap tool to snap to the actual intersection in two or more entities. How To?