The "contact form" switch at Admin Panel -> Settings -> Switches enables a contact option whereby your site visitors can send you a message. The contact link is normally at the bottom of the page. When the switch is enabled, you can configure who's notified of the messages (or send them for a special forum instead of email, in WSN Forum) at Admin Panel -> Settings -> General -> "Contact Form:".

If you want to allow people to attach a file to the contact form, see emailing files. To add other custom fields to the contact form, see custom email form fields.