CiviMember can be used in conjunction with your CMS to create a members-only section of your website. Each CMS has it's own integration module(s) that can be used to do this. A typical workflow would be that a contact creates an account on your site and becomes a member of your organisation using a CiviMember membership sign up page. When they log in to you site they get access to member-only content on your site. This extra content could be from your CMS or it could come from your CRM, for example a detailed members directory, or a list of private events that are only available to members. You can refer to the section on your CMS in Website Integration for more information or ask questions on http://forum.civicrm.org/.