When you archive, that Yapp is deleted off of users' devices and will appear in a special archived section of your dashboard.
To archive an app, click the gear icon in the card on your dashboard.
The app will then move to the Archived section, which you can access by clicking "Go to Yapp Archive" in the bottom right corner of your dashboard.
There, you can see all the apps you've archived. You can reactivate or clone the app.
Reactivating an app will count it towards your plan limit. See more about how plan limits work.