coding problem

Use code tags:

Format your stuff so we don’t have to struggle to read it.

Finally, did you read the error:

You use the Command attribute:
https://docs.unity3d.com/ScriptReference/Networking.CommandAttribute.html

This is part of the Remote Actions system:
https://docs.unity3d.com/Manual/UNetActions.html

And if you read through it you’ll see that just like the error says, the script PlayerShoot should be inheriting from a ‘NetworkBehaviour’ when you use it. Not from a MonoBehaviour.