If you want to close your store temporarily (for ex. during tests), please do the following:
1. Open the StoreFront Control Panel.
2. Go to the System Settings → General → Store Profile page.
3. Click "Close the Store for Maintenance" button.
4. You may want to be able to still be able to see your store. In such case, insert your IP address into the "Remain open for the IPs" field (your current IP address is written below that field).
5. After that your store will be closed for all visitors, but you'll be able to browse it.