The primary function of a web server is to deliver web pages and associated content to clients. A client, commonly a web browser, makes a request for a specific resource using HTTP protocol and the server responds with the content of that resource. The resource is typically a real file on the server or the content generated by the server.

While the primary function is to serve content, a full implementation of HTTP also includes a way of receiving content from clients. This feature is used for submitting web forms, including uploading of files.

Many generic web servers also support server-side scripting. This means that a script can be executed by the server when a client requests it. Usually, this functionality is used to create HTML documents on-the-fly as opposed to return fixed documents.

A web server has defined load limits, because it can handle only a limited number of concurrent client connections per IP address and TCP port. It can serve only a certain maximum number of requests per second depending on (a) its own settings (b) the HTTP request type (c) content origin (static or dynamic) (d) the hardware and software limits of the Operating System where it is working. When a web server is near to or over its limits, it becomes overloaded and thus unresponsive.