Now there are the two main ways of getting around Brighton that being the Train services and then there are the bus routes.
For trains a normal ticket from Falmer (Closest station to Sussex university) costs at the moment £2.90 with a rail card that costs £28 you can get the price down to £1.90 for a return ticket that's a very good price if you just want to go to the shops, But the trains stop around 11 o'clock so if you want to go drink within Brighton then buses might be for you.
There are two main bus companies the lemon bus and the Brighton and Hove buses. Now there are a few big differences between them firstly price currently it is £2.50 for a all day pass with the lemon buses and that is preferred by many students and stops at some good locations but they are less frequent so you could be waiting a while.
The Brighton and Hove buses are a more frequent and have more stops but they cost £3.70 for a day pass but there are all week passes available for £10 at student union shops.
So in conclusion if you want to just visit town once or twice in the week without going to the supermarket go with the train services.
If you want to go drinking and have all the food you need then take the lemon bus
but if you think you will be travelling between your campus and town frequently get the Brighton and Hove buses they go to most places and are the most frequent with good deals on all week travel (oh and if you want to buy a all week pass buy it at a student union shops, if you buy on a bus it might be specific only to that particular number of bus and your area of travel will be cut short)