To return something to its original place.
He carefully put the vase back on the shelf.
To turn back; to return.
To postpone an arranged event or appointment.
The meeting has been put back to 5.00 pm.
To drink fast; to knock down alcohol.
You'll need to put that drink back quickly; it's very nearly closing time.
To change the time in a time zone to an earlier time.
Don't forget that this Sunday we put the clocks back an hour.