Florianópolis is a city of beaches, with over 23 different beaches, really this island city is all beaches, but they are among the best in Brazil. The night life area consists of several clubs on a long strip of land between the city and the beach.
There are a surprising number of Florianópolis hostels, located both in the city and by the beaches. Be aware that the small strip of land that connects the city to the beaches is jammed during rush hour starting around 4 PM and it could take you over three hours to get back to the city instead of the normal one. So you may want to book a Florianópolis hostel near the beach, as staying in the city and taking the bus (and changing to a 2nd bus) gets old after a few days. Plus the views from most of the Florianópolis hostels near the beach are breathtaking. Most of the hostels allow you free use of surf boards and other water equipment, so you can try your luck with surfing as well.