A VPN app on an iPhone secures your device's internet connection by routing all traffic through an encrypted tunnel to a remote server. This hides your real IP address and prevents anyone on the same network, like at a public Wi-Fi hotspot, from snooping on your data. It's particularly useful for protecting sensitive information in apps like Mail or Safari. Additionally, it allows you to bypass geo-restrictions, enabling access to streaming libraries or websites that may be blocked in your current region. The app integrates directly with iOS, showing a "VPN" indicator in the status bar when it's active.