The Traveline website says that you should walk to the bus station (3 minutes). Take Stagecoach South service 1 to 'Montgomery Lines, Queen's Avenue Church'. (Buses run every 10 minutes. The journey time is just 4 minutes). Then walk to Buller Barracks (11 minutes).
That will all make much more sense if you go here:
http://www.travelinesoutheast.org.uk/se/XSLT_T RIP_REQUEST2?language=en&timeOffset=15
Select your date & time of travel.
Ensure that the pull-down menus both show 'Postcode'. Enter the two postcodes where it says 'Location name'.
Click 'Submit'
Then click 'Show These Route Details'.
Finally, click 'Start Map' (if you think you need it) and 'End Map' (which shows how simple that 11 minute walk is).
Chris