Selling a car is pretty easy. If you're selling it with rego you'll need a RWC. Once you have the RWC and a buyer, all you have to do is fill in a transfer form (available from vic roads) and take the cash.
If selling without rego, you need to take the plates off the car and write up a contract of sale. It should contain vin & engine nos., sellers full name and address, buyers full name and address, amount being sold for, date of sale, etc, etc.
Call Vic Roads 13 11 71 and they'll give ya the full details.