To log in to a protected network, you need a VPN connection. This is usually the case when you want to access a company or university network. How to set up a VPN connection on the Samsung Galaxy S9 within Android is described here:
How to use VPN on the Samsung Galaxy S9
1. Open the app menu from the home screen and then the Android system settings.
2. Click on "Connections" and then on "Further connection settings".
3. Scroll down and you will see "VPN".
4. Touch the menu entry and you can now create a VPN connection by tapping the plus symbol
5. You now need the data from your VPN network - enter it and then save the new access
You have just created a new VPN connection on your Samsung Galaxy S9. Via these you can now log into your Virtual Private Network.