Restricting background data on a Samsung phone means that apps will not use data unless they are active in the foreground or connected to a Wi-Fi network. This can help reduce data usage and save battery life. Here are the steps to restrict background data on a Samsung phone:

1. Open the Settings app.
2. Choose Connections in Settings.
3. Enter Data usage.
4. Enter Wi-Fi data usage.
5. Choose an app.
6. Deactivate Allow background data usage.

Alternatively, you can go to Settings > Connections > Data usage > Background data, find the app you want to restrict, and click the toggle next to it to deactivate its background data usage. Restricting background data on even a few apps can significantly reduce overall data usage. However, its important to note that restricting background data may cause some apps to stop functioning unless a Wi-Fi connection is available.