C API?

Question

I took AP Java and passed the test with a 4 and now my teacher is planning to teach a follow up class next year using C# and from the looks of it, instead of import, its using but I can't find the API for it or if I did, it's completely different from the java API. I have a very short but nice kingdom hearts mini game that I would like to convert from java to c#, but I can't find the classes to import them. Oh and if anyone knows a website that shows clear and distinct difference in java and c# (though from what I've seen so far, it is not much), I would appreciate it o.O