Help? Strange bump on puppy's belly?

It's a little hernia, A lot of puppies are born with little hernia's. Most of the time they'll go away as they mature. It can be removed by a vet, usually just for cosmetic reasons. I wouldn't worry about it unless it starts getting bigger. You could push it inward and hold it in for a while each day 5 to 10 min. a day and this should help it go away.