A thumb latch is a simple type of door latch usually used for gate doors -- not exactly the most secure type of latch. Though it won't keep people in or out of your gate, a thumb latch will help keep pets in and strays out. When you decide to go with a Stanley thumb latch rather than any other brand, you get the guarantees that Stanley gives with their products.
Grab the door handle with your hand.
Pinch the thumb latch with your thumb. This will unlatch the door.
Pull the door toward you to open the door.
Close the door behind you and the thumb latch will latch the door in place.