It is a physical place where people can physically go and use the net. Internet Cafes have been in actual cafes. Places that serve coffee and other things that go with it. But an Internet Cafe could be a restaurant, a bar, even a bowling alley. The key is that it is a place where people can go and use the Internet in a social amosphere.
Internet Cafes serve a number of purposes.
First it is a place where people can socialize and enjoy the atmosphere while they surf the net. Second it provides Internet access for those who do not have it elsewhere. Frequently Internet Cafes have training and help available for the new user. This second purpose is an important one. When the World Wide Web came into existence it became possible for people who were not technically trained to access and use the resources available on the net.