To install a door stopper on a wall, first, choose a location where you want to place the door stopper. It should be close enough to the door so that it stops the door from opening too far or slamming shut, but far enough away from the hinges so that it doesn't interfere with the door's movement.

Next, mark the spot where you want to install the door stopper. Use a pencil or other marking tool to make a small dot on the wall.

Then, using a drill and screws, attach the door stopper to the wall at the marked spot. Be sure to screw it in securely so that it doesn't come loose over time.

It depends on your specific needs. Some common places to put door stoppers include behind doors to prevent them from hitting a wall, on the floor to prevent doors from swinging shut, or on the back of doors to prevent them from opening too far and hitting a wall or furniture.

Ultimately, the best place to put a door stopper will depend on your unique situation and needs.