You can use the provided Unlock url to access your site directly, or enter the Key at the URL of the site.
The Unlock URL can also be shared with any visitors that you wish to have access to the site.
You can use the Access key panel to generate a key which is needed to enter your site.
The access key is useful when developing websites to allow you access for testing, while barring any other visitors from accessing the site until you're ready.
The first time that you visit the site with an access key it will be stored as a cookie in your browser. After this, you can continue visiting the site without needed to enter the key again - providing the key stays the same.
This allows you to work on your site while your URL is live or test your site by giving the key to a select few testers ahead of public launch.