In addition to the other replies:
You have to decide for yourself which Anti-Virus program you want to use.
Choosing an Anti-Virus Program
Supplementing your Anti-Virus Program with Anti-Malware Tools
What’s the Best Antivirus for Windows 10? (Is Windows Defender Good Enough?)
If you want to use Norton, Windows Defender should be automatically disabled as soon as Norton is properly installed.
Norton and Windows 10: https://support.norton.com/sp/en/us/home/current/solutions/v107701320_EndUserProfile_en_us
If you want to use in-built Windows Defender, you need to uninstall Norton and then run the Norton Removal Tool to get rid of all remnants (https://support.norton.com/sp/en/us/home/current/solutions/kb20080710133834EN_EndUserProfile_en_us)
Reboot and Windows Defender should be enabled.
If not, try: Windows Defender - Turn On or Off in Windows 10
Configure Windows Defender in Windows 8, 8.1 and 10
How to Use the Built-in Windows Defender Antivirus on Windows 10
For further Norton help I suggest you ask in the Norton Forum: http://community.norton.com/en
Cheers,
J