This puts a Passing-On icon on your phone, right next to your other apps. You tap it to open — same as any app, no browser address bar, no typing in a web address. It takes less than a minute and there is nothing to download from an app store.
It's just a faster, simpler way to get back into your vault — one tap from your home screen instead of opening a browser and typing an address. Nothing changes about how your information is stored or protected.
Prefer to just use it in your browser? That works perfectly fine too — installing is entirely optional.