Can I hide my site from people while I add my content?

Short answer, yes!

If you don't want other people to see your site as you're working on it, you could go with a maintenance mode plugin like:  https://wordpress.org/plugins/wp-maintenance-mode/.  If you activate this plugin, make sure to go to the settings for the plugin and configure them how you'd like (mainly turn on maintenance mode). 

With this plugin installed, you must be logged in as the admin in order to view the site. 

PRO TIP: we'd recommend turning off maintenance mode when you run your test purchases so that you can truly experience the site as your customers will.