Teaching Tips: STEP 1. Introduce the bell to the dog. Let them feel it by sniffing it. let them hear the sound of the bell.
Encourage its interest by giving her treats and show your appreciation that it knows you use it only when she does a good job (like good girl, my man.. good job etc.)
STEP 2. Second stage is to get your dog to ring the bell. For this you can take the bell outside and show you how to ring the bell. You can use the family environment she is comfortable with.
Every time it rings the bell gives her a treat. Few dogs do better with a lot of attention; they get distracted. So please choose the set up based on your dog's nature.
STEP 3. Now place the bell where you intend to place it. Like hanging it to your backside door where you normally let the dog out.
Ensure the bell is firmly attached so that it doesn't fall out by a simple tug/pull which might scare them. Again positively reinforce your appreciation with treats and words when they ring, do open the door and give her a treat when it goes out the door.
STEP 4. It is time to make it a habit. If you used to let your dog go outside once you are up to let it potty/pee, use the same setup but this time make your dog ring the bell.
Reward once it rings the bell and steps outside. Keeping repeating this process until it becomes natural for the dog to ring the bell is the natural way to ask to be let out.