The primary purpose of a web browser is to retrieve information resources and to display the information to the user. When the user inputs a Uniform Resource Identifier (URI) into the browser, the browser will determine how the URI will be interpreted. For example, the http: in the URI http://en.wikipedia.org/ identifies the resource to be retrieved using the Hypertext Transfer Protocol (HTTP). Many browsers also support a variety of other prefixes, such as https: for HTTPS, ftp: for the File Transfer Protocol, and file: for local files. Prefixes that the web browser cannot handle are often passed to another application entirely. For example, mailto: URIs are usually passed to the user's default e-mail application, and news: URIs are passed to the user's default newsgroup reader.
In the case of http, https, file, and others, once the resource has been retrieved the web browser displays it. HTML is passed to the browser's layout engine to be transformed from markup to an interactive document. Aside from HTML, web browsers can generally display any kind of content that can be part of a web page. Most browsers can display images, audio, video, and XML files, and often have plug-ins to support Flash applications and Java applets. Upon encountering a file of an unsupported type or a file that is set up to be downloaded rather than displayed, the browser prompts the user to save the file to disk.
Information resources may contain hyperlinks to other information resources. Each link is associated with a URI that, if clicked, is used to retrieve further resources. When a link is clicked, the browser navigates to the resource indicated by the link's target URI, and the process of bringing content to the user begins again.