the gist is that if you want to just vote for a party, you can: if you simply put a 1 in a box, that party will assign your preferences (when you vote “below the line” - numbering every box in the order that you’d like - you have to fill out 150 numbers, making sure you don’t make a mistake)
so your ballot paper has about 20 different parties[1] on it, ranging from the major parties (coalition/liberal/national and labour) to a few others (greens are becoming big, socialist alliance, etc), and then single issue parties (legalise cannabis australia, there was a high speed rail party at 1 point)… and it has a bunch of individual politicians below each party with their own boxes
if you decide that legalising cannabis is the issue you care about, you can just number their box and they’ll allocate your preferences - hopefully based on how likely they think a particular politician is to support legalising cannabis. you can also put multiple numbers above the line and a range of other things, but at its simplest it’s putting a 1 in a box and going home
some of this might be slightly incorrect because it can get very complex and i don’t really delve too deep into how the ballot actually works at its most complex level… but i think the great thing is that you can vote according to whatever complexity or detail you like and the system ensures your vote is allocated to who you’d most likely want