There are bus timetables and maps available but if you have online access, here is a very useful journey planner. You plug in an address, location or postcode for your start and end locations and it will give you several of the best options for getting there, using a combination of walking, busses and trams and approximate time it will take to complete the journey. You can also look up a bus number and it will give you the timetables.
You can also get the time of the next bus texted to your mobile phone. On every bus stop sign there is a code on the bottom. You text that code to 84268 and you will get a reply with the time of the next busses. There's a 25p cost for the service.
You can download a pdf file for the timetable for any bus number, on this website