Hey there monsterx,
An honours year is a fourth year of a bachelor's degree. It is not available to all students- traditionally those with all or mostly marks above 80% were invited to undertake an honours year. For almost all disciplines it consists of half advanced coursework, and half research thesis of about 10 to 15 thou words. Law is an exception, I think, where coursework alone may comprise an honours year.
The "class" of honours awarded is the assessment or mark- first class would be awarded to those with a mark of either 80 percent or above, or 90 percent or above, depending on the University.
A first class honours degree or a Masters by research is considered appropriate entry qualitification for a PhD. For students without an Australian honours degree it is likely that the admitting School or Faculty will want to read and assess the research thesis, or a part thereof.
Thanks, looks like I have to tick "no" and explain in the text box.