The first time users click on the download link, a pop-up will be displayed on their screen to confirm that they want to download the application. Then, the first time it's launched, a new pop-up will appear. iOS will ask them if they trust the distributor of the app, which in this case is you.
To confirm this and in order for the app to be usable, they will have to go to the menu Settings > General > Profiles and Device Management in their iOS device. Your users will then have the pleasure of exploring and using your beautiful app!
