You can specify an object snap whenever you are prompted for a point.
By default, a marker and a tooltip are displayed when you move the cursor over an object snap location on an object.
To specify an object snap at a prompt for a point, you can do following:
When you specify an object snap at a prompt for a point, the object snap stays in effect only for the next point that you specify. Object snaps work only when you are prompted for a point.
If you need to use one or more object snaps repeatedly, you can turn on snap, which persist through all subsequent commands. For example, you might set Endpoint, Midpoint, and Center as running object snaps.