With the appropriate club, chip 5-10 balls from off the green. Imagine you are playing a par two hole. If you chip it in you get a birdie. If you do not make your next putt you bogey the hole.
After you chip, start with the nearest ball to the hole, and with your putter attempt to hole each one out. This helps simulate the pressure of an actual game situation.
Try this as a competitive game with a practice partner. The fastest way to lower your handicap is to spend your practice time chipping and putting.
Purpose
To improve your short game. Getting up and down is the surest way to start lowering your score. You can make up for earlier poor shots on the hole. It can also be devastating to your opponents.
To simulate pressure situations. Simulating pressure situations allows you to practice improving your concentration. You should be concentrating on your next shot and therefore the positive actions that you need to make that shot successful. That takes mental focus, which is something that must be learned and practiced.
To practice competitively. When you do this drill (or game) with a practice partner.