There are currently two bus services in GWP, both are provided by Thames Travel.
The 98 runs Monday through to Saturday, please note it does not run on a Sunday.
Timetable is available here https://www.thames-travel.co.uk/routes/98
There is also the late night NX2 service which runs Monday through to Saturday.
Timetable is available here https://www.thames-travel.co.uk/routes/x2