How do I program an nine-mens-morris game with AI in C#?

If you aren't familiar with C#, then you have probably selected a project which is far too advanced: Nine Men's Morris is a deceptively simple game and it will take some serious work to get an AI opponent working at all, much less competently!
And while there are many tutorials on C#, you will not find one specifically implementing NMM for beginners!

Start smaller: you are presumably on a C# course, or the assignment would not have been set. So read your course notes so far and do the exercises up to this point. By then, you should have a good idea how C# (and the .NET framework behind it) works and be able to at least start this project.

Without that? You will get nowhere - this is not a project for a beginner - I'd have to set aside a significant amount of time to implement it, and I play NMM from time to time already!

Quote:

I have a school project where I have to program a Nine-Mens-Morris game with AI in a WPF application. I have no idea how to program in C#

I find it hard to believe that your teacher could expect you to create such a project. The learning path for C# is not something that can be done in an afternoon. And the learning path for WPF is considerably more advanced and requires a detailed knowledge and experience of both C# and the .NET framework. And then you have to learn AI, in order to implement the actual game.