I just got a 11-15 oyster card, how do i insert it into a bus & also do u have to put muny in the oyster card?

i just got an oyster card and im not sure how to put it into a bus,The oyster card is 11-15,so do i have to put money into it??Cus on Youtube i see ppl puttin muny credit on thier oyster card.I live in London.