A nice way to get to know St. Gilgen and surrounding places at the Wolfgangsee is to go by boat. We parked our car in the quiet town of Strobl on the other end of the lake and took the boat to St. Gilgen passing St. Wolfgang.
A Daycard for a family is € 34,00 per family of 2 adults and 2 children. You can take the boat is often as you want. Nice, relaxed boating on Wolfgangsee.
There is a bus route between Salzburg and Bad Ischl that runs along the southern shores of the Wolfgansee. St. Gilgen is the first stop along the lake. You can also catch a bus directly from Bad Ischl.
Or, if you're really lucky, you can get a ride from a kind-hearted VTer like I did.
From the bus station, it's a short walk to the right down Schwartzenbrunnerstrasse to the main square.