Configure Xamarin.Android on VSO

Hi
I'm setting up a CI build with VSO for my Xamarin.Forms (Android) app but I have a lot of error. I would appreciate if someone tell me how I can configure xamarin.Android build step.
what should I address in the project field? should I give project sln or in the .Droid folder .csproj ?
I could not find any document about this configuration.