1) To "bang on" something is to hit it. If you are banging on the door, you are knocking extremely loudly. If you are banging on the vending machine to get the stuck item out, you are hitting the vending machine. You can take a hammer and bang it on a nail to drive the nail into the wood.
2) To be "bang on" is to be accurate, and means approximately the same thing as "hit the nail on the head". One could use it in a sentence such as, "You were bang on when you said I'd enjoy that wine, mate."
3) To "bang on" means to speak at length. You could say, "She did bang on a bit, she just wouldn't shut up!" or if someone is speaking a lot but making no sense, you could say, "What are you banging on about?"
4) "Bang On" is an Australian podcast featuring Myf Warhurst and Zan Rowe, in which they debrief and discuss with each other the various conversational topics of the week. Episodes usually cover a few things in the latest big news in politicals, social, and entertainment, plus something they have each been interested in recently, such as a TV show, book, news feature, or famous person's activities. The first podcast episode was published on 9th March 2017, with the "coming soon" promo published on 1st March 2017. There have been 38 episodes published to date, with the latest one released on 23rd November 2017.