You can find all connections by bus and train at: www.oebb.at/en.
You can get to some places only by bus (Postbus). For example Mondsee, Wolfgangsee.
From lake Wolfgangsee to Hallstatt take bus nr 150 till Bad Ischl and after the train (if you take bus for this journey it takes longer and you have to change once)
Best regards, Beatriz