In Xamarin Studio or Visual Studio for Mac (VS4M), when creating a project, you will have a drop-down option for the language of this project, which is located to the right of the project type: C#or F#or even IL(depending on the type of project).

Select:
C# for ordinary programmersF# for programmers who really hate classesILintended only for real programmers, if you should ask ....; -)
, Addins (Extensions VS4M), :
