To put your store in 'Maintenance' mode go to Settings> Store Settings > DIsplay > Store Closed.
- You can also configure a custom store closed page to display for any customs who get to your website while this mode is enabled.
- You can re-enable by clicking Open Store at the top of your admin.
- You can also click on View the store as a customer or admin
- This is useful if you wish to use this as a type development mode.