I'm using MSVS2015Pro for Xamarin.
I downloaded the project: https://github.com/Clans/FloatingActionButton
But I'm getting an error on:
Severity Code Description Project File Line Suppression State
Error CS0246 The type or namespace name 'Clans' could not be found (are you missing a using directive or an assembly reference?) FAB.Sample D:\Xamarin\FloatingActionButton-Xamarin.Android\FAB.Sample\FloatingActionMenuBehavior.cs 5 Active
PM> Install-Package FAB.XamarinAndroid
You should not have to troubleshoot these kind of problems very often.
Visual Studio projects you download from github should contains all external references pointing to nuget packages and you restore them on first build (unless project is not configured to restore on build).
Local references are either framework references you should have installed on your machine or other projects inside the solution.
Normally a missed class will be paired with a yellow exlamation symbol on references list indicating that a necessary assembly could not be loaded, that could be a first check to do.
Output window from build could also provide insights about any anomaly related to references.