I will give you the most common way, if this does not help you will need to resubmit with the model number. Also make sure the keypad has good batteries on it.
On the opener motor housing you will find a colored learn button. It will be the only button you can actually push, and will be green, red white, purple or orange probably. It will be on the back(single light) or the side(double light) of the unit. Push this button and within 30 seconds enter the 4 digit code on the keypad followed by the up/down button. The light bulb on the opener will flash once. This tells you that it has accepted the device. If it does not flash and the batteries in the keypad are good and the remotes work then you need a new keypad. If it does not work and the remotes don't work too then you need a new logic board. These items can be found on sears.com. Have the model number ready. Thanks BB