Money

" Money. You don't know where it's been, but you put it where your mouth is."

This line means that people see money has a way to bond. An example is how men go to the football games to bet on their teams and how much they are going to win by, they are actually bonding. The saying, "put it where your mouth is" means that when people have money their actions speak louder than words, they do brag about money, but also they put it to the test, like gambling with friends.
The phrase, "you don't know where it's been," means that your money was lost, because you could of spent it all on anything cloths, bets, etc. Now you found the money by your savings or just staying away from the boys with the football games. Now you are able to put it where your mouth is like betting and hanging out with your friends again.