USU runs most student services, cafes, bars, clubs and societies, blah blah blah. It's run by a permanent staff, but they also have a board made out of students as a sop to student representation. Half the board is elected each year. Almost all the candidates are hacks from one political party or another, although they try to obscure this because it would drive turnout even lower than it already is. Most are from the labor left (which you'll see referred to as the labor club or NLS, national labor students; it's the biggest faction and its candidates, who this year are Bec and Alex iirc, are basically guaranteed election because they have more money and campaign worker bees than the others), the labor right (alp club or student unity) or the young liberals.
It pays to be cynical when choosing who to vote for because the odds of anyone following through on their grandiose campaign promises are extremely minimal. For some of the candidates this is because they've just come up with them in a transparent attempt to attract votes and don't intend to do anything about them. For others it's because they're full of ideals but will realise once they're on the board that there's nowhere near enough money to do all the crap they want to do. For others it's because their platforms are so vague (activate! participate! create!) as to be meaningless. In any case, significant numbers of them only want to be a director for the line on their resume because they think it'll help them become an MP.
Vote counting is by proportional representation, but as far as this concerns the voter it just means you number the candidates in preference order, as in a federal election. There's an affirmative action policy which means that a certain percentage (half?) of those elected must be female.