Vacation mode prevents people from purchasing products, while still being able to browse your store!
You can enable Vaction Mode inSettings Click site and scroll down to Sitewide Messaging and Vacation Mode
Sitewide Message
Directly below vacation mode, you can enable a sitewide message. This goes very well with vacation mode, as you can make it clear that your site is on vacation mode, as well as let your customers know how long you will be on vacation.
Vacation mode is not required to have a sitewide message, you may enable the sitewide message at any time and have it contain whatever you like!