If you try to add reference to your project, you should have a bunch of ESRI namespaces. ESRI.ArcGIS.ArcMap should be one of them. If you have none of the ESRI.ArcGIS ones, the .NET support is not installed (if you have installed ArcGIS before the .NET framework this will happen.) You can verify this by looking for the "dotNet" folder in you ArcGIS installation folder. If it is missing, you need to run the installer again and make sure the .net support is installed.