An intranet is a private computer network used to share part of an organisation’s information or operations with employees or partners; it is a website or websites, maintained internally, that are only accessible to authorised users.
Windows SharePoint Services or Sharepoint provides the means to put together an intranet. You can install SharePoint through the ‘Add/Remove Programs’ in Windows Server 2003 R2 or you can download the latest version compatible with your server OS from Microsoft website.