Servers, as their name suggests, provide a service. This can mean a wide variety of things. Some servers are configured for file storage (i.e. NAS [network-attached storage], FTP [file transfer protocol]), while others specifically respond to requests to provide content (such as Web servers [you're making use of one now if you're browsing the Web!]). Some can be used for managing network traffic (e.g. a corporate intranet) as seen in enterprise or large-scale business set-ups.