Open parkint.org in Safari, then:
It has to be Safari - other browsers on iPhone cannot do this. You get a Parkint icon that opens full screen with no address bar.
From the browser:
For most people, installing from the browser is the better option. It updates itself, takes almost no room, and works the same on both kinds of phone.
Parkint is not in the App Store or Play Store yet. We will put it there once there are enough parking lots on it to be worth downloading.