The Visibility card sits beside Site Information on Settings › General in the admin. It holds three switches, each with its own one-line explanation right underneath it. Remember to click Save Settings at the bottom of the page.
This is the on and off button for your entire site. If checked, this site is live. If unchecked, access is disallowed for all users and admins.
If checked, members can see your prize store. If unchecked, the store is listed as "coming soon."
When checked, the general public can register for your program. If unchecked, non-members will not be able to register an account. Programs that are exclusive to a particular group — season ticket members, for instance — usually leave this off.