If you are just dipping your toe in the water when it comes to testing .NET applications it can be a bit confusing. In addition to learning how and what to write test, you also have to learn a testing framework such as MSTest, xUnit.net, NUnit, etc.
My new beginner Pluralsight course helps you to get started with testing in .NET and how to use the NUnit testing framework.
Watch the course at the above link or get to it from my Pluralsight author page.
You can start watching with a Pluralsight free trial.