About Private and Public Apps in Blocks
Wix Blocks is open to all Wix Studio users. To access Blocks, go to Custom Apps in your Studio workspace.
When you build an app with Blocks, it can be private or public. Private apps are apps that you plan to use on your own sites or on client sites. Public apps are apps that you plan to publish in the Wix App Market. So, the difference is in on how you plan to use the app. Note that the same app can be used both for your private use, and for publishing in the App Market.
Private Apps
Private Apps are created to be used on your own sites, or on your clients' sites.
You can install these apps on as many Wix sites as you want, as long as you are an owner or collaborator to the site. Enjoy the benefits of reusing the app's user-interface, code, collections and dashboard pages.
To install one of your apps on a site, go to the site editor, click the 
icon, then click Custom Apps and search for that app. You can also go directly to Custom Apps and select a site from there.
Learn more about installing your private apps.
Public Apps
Public Apps are apps that you intend to publish in the Wix App Market, where they are visible to millions of Wix users. You can choose to offer your apps for free or sell them.
When building an app with the intent to publish it, you will probably need to adjust its structure and logic to different pricing plans.
To install one of your public apps, users can go to their site editor, click the icon, then click App Market and search for that app. Or, they can go straight to the App Market website.
Learn how to publish your app in the App Market.