""An unhandled exception of type 'System.NullRef erenceException ' occurred in WindowsFormsApp lication2.exe

Additional information: Object reference not set to an instance of an object."

I am new at programming and I don't really get the explanation that I saw on the sites.
When I am going to use a Button.performc lick operation, I do get this problem. I clearly do not see any problems in my code but please...