I trained using the bell and now regret it, I'll explain why after. Every time I took my puppy out I would have her use her nose to bump the bell (if you train with them using there paws to bump the bell, expect your door and wall to get scratch up worse than what the bell does by itself). After I would help her bump the bell with her nose, I would praise and take her out side. Just keep repeating until your puppy does it on there own. Each time they use the bell get super excited and praise and take them immediately outside. They will pick up on it very quick as long as you make it positive and keep at it.
Why I wish I didn't train with the bell... Once my puppy figure it out, she also figured out if she rang the bell she got to go outside. Well, she started asking every 10 minutes to go! LOL! That is easy to figure out when she is needing to go out or being a brat. It is annoying when she would do it just to do it. You try to make it so a positive potty trip and she abuse it! Hehehe! She still uses the bell to this day, she is now 1-yrs old. But the bell has seriously left some dents in both the door and the wall next to the door, she rings that thing like no one can hear it. That is one of the reasons I wouldn't have your puppy use there paw to ring, it will only add to the damage the bell will do.
If I had to do it all over again, I wouldn't use a bell. I did find this product that is meant for this thing and it won't do the damage a normal bell would. Check it out and good luck with the training!