To implement delegates, the necessary condition is?

Class Declaration in implementing delegates is important.
Delegates types are declared with the delegate keyword. They can appear either on their own or nested within a class

Example:

namespace DelegateTest

{

    public delegate string FirstDelegateTest (int x);

    

    public class Sample

    {

        public delegate void SecondDelegateTest (char a, char b);

    }

}