What is the purpose of specifying the return type of a class for a delegate and a function?

Question

C++ / C#

I don't understand how it works, why do we specify the return type of the class? Explain to the fool in simple terms, please, how it all works.
PS - This is the 6th chapter of the metanit. Covariance and Contravariance

Answer 1

why do we specify the return type of the class

Well, so that we can return a value with this type from the method.
Try not to specify, or specify the wrong one, and you will get a compilation error.

Answer 2

To understand what kind of type they return to us, everything seems to be obvious. You do not just create EmailMessage there.