At the front of the buss you can get change from a bill. do this before your stop comes!!! while the bus is in motion. you will make everyone on th ebuss very angry if you do it while you are getting off. you must pay in the exact abount and drop your ticket in with the money.
when you get on a Bus in Japan don't forget to grab a ticket out of the machine or put in your bus card in the green slot. almost every buss in Japan looks the same in this respect.