Well you didn't give any links to what you're referring to, but I'm going to guess the server is C#. Also, if you're curious because you want to learn programming, it really isn't necessary for this kind of work. You'll progress a lot quicker by learning how these servers work.
There are a lot of newcomers who don't understand the functionalities of what's in front of them. If you don't know types, variables, operands, conditionals, and the basic fundamentals that you'll be using during development of a private server, then some programming courses would be beneficial.
Even then, if you understand the basics, without proper knowledge on how servers function, you won't be able to make much progress in development.
Just to add, clients are AS3, which is a lot of fun to work in.