From what i grasped
Theres the 391, 393, 395 which are the normal buses and the 891 express bus
You get off when you see this massive long walkway which is anzac road entrance to the uni. But just follow the asians LOL
if you catch the 891, like someone said, it will drop you straight at the uni, no stops in between. and like this person said, just follow the crowd heading into the uni (you'll end up outside the uni itself and will then walk through some carparks etc). do what i did - pick someone who looks like they know where they're going and just follow them, lol.
if you catch the 391, 393 or 395, these will stop at many places between central and UNSW. as far as landmarks go, i've found the most helpful ones to be the big NIDA building (looking out the right-hand side of the bus - big brick building with a massive 'NIDA' sign, you can't miss it), and the UNSW sign itself, which has lit-up scrolling text and is in amongst lots of greenery (you see this out the left-hand side). once you pass NIDA and the UNSW sign, get out at the very next stop, and once again, just follow everyone else.
alternatively, don't worry about landmarks, and just wait until almost the entire busload of people suddenly gets off the bus, and follow.
i'm sorry if this sounded patronizing or really obvious...but i had the exact same sorts of worries (i started a month ago for a bridging course), so i hope this has helped