Use the company's own app listing
Create the account on the provider's website, or start from the app listing that same company publishes in the App Store or Google Play. Skip download buttons in email, search ads, and other websites. A lookalike listing is a common way to install a different app under a familiar name.
On iPhone the listing is in the App Store. On Android it is in Google Play, unless the provider also publishes an install file and you chose that file on their site on purpose.
Accept the VPN prompt only if it names your app
Open the app and sign in. iOS asks to add a VPN configuration. Android asks permission to set up a VPN connection. The system dialog should name the app you just installed. If it names something else, cancel and go back to the store page.
That prompt is the operating system handing the app the right to carry your traffic. It is a normal step for every VPN, and it is also the step worth reading.
Confirm the address changed
Tap connect and wait until the app shows a connected state. Then open a page that prints your public IP address. The NetPulse IP address tool is one. The address should differ from the one you saw before connecting. If it is the same, the tunnel is not carrying your traffic. Disconnect, quit the app, and try again before you rely on it.
Kill switch, in plain words
Some apps have a kill switch, or a setting with a similar name, that blocks internet access if the tunnel drops. Turn it on when you would rather the phone go quiet than fall back to the open network. The label varies by app. The provider's own setup guide is the place that matches their label to that behavior.
Disconnect, and the device cap
Disconnect in the app when you want the normal connection back. Removing the app later works like any other app. On iPhone, if a leftover entry remains, it sits under Settings, General, VPN and Device Management.
You can usually install one account on more phones than can be connected at the same time. If a second phone reports that the connection limit is reached, disconnect the first or check the cap on our compare page.