Before building the solution you will need to copy your Sitecore.Kernel.dll from your project into the Library folder. This is not included in source control for licensing reasons.
The project builds against .NET 4 to allow compatability with the widest range of Sitecore versions, because of this, the Sitecore.Kernel.dll you use must be version 6.x or below, as Sitecore 7.x is built against .NET 4.5.