I have an Australian travel document for refugees. Do I need a visa to travel to Germany? From there, will I be able to travel to Belgium ?
The answer is no, you don't need a visa to go to Germany with your Australian Travel Document.
From the Germany embassy in Australia:
The same applies to holders of Australian travel documents for refugees (Convention of 28 July 1951) and stateless persons (Convention of 28 September 1954): They can enter Germany without a visa for an intended stay of up to 90 days, as long as at the time of entry into Germany their travel document is still valid for at least 4 months.
Once you're in Germany you can freely travel in the Schengen area which includes Belgium.