With buses within the city centre, they have a flat fee of 230. You get on the bus from the back door. If you are taking a bus that will go outside the city centre (like to Takao) that is when you get you take a ticket as you get on that will tell you how much you have to pay. Then when your stop is coming up press the red part of the button next to your seat or on the pole. There are screens at the front of the bus where you can see the next stops in both English and Japanese.
When you are getting off drop your change in the slot in the machine next to the driver (1). If you do not have change then you can put a 1000 bill in the lower yellow slot for change (it gives you both 100 and 10 yen coins) (2), you can also get change for 500 yen (3), the change will come out into the both cup (5). If you have a card put it in the upper yellow slot (4).