There has to be a modem somewhere - either the apartment complex is providing the wi-fi, in which they would have a modem and access points installed in the buildings, or you have a modem to connect to them. If you are looking to create a network, under the first scenario, you would need to install a router that is a bridge to their network - and via wired or wireless connections your network would be setup.
How do you connect to the Frontier wireless network?