How do I use a .cs file ?

Hi,
Wanted to add reviews to my website and thought instead of coding something, I would buy something off the shelf.
Found a company and they have supplied me a .cs file. I have no idea what am suppose to do with this file. The help they give ain't great and basically they say do a import namespace, create a object and call the object.print method.
Uploaded everything to my server but am not even getting past the import namespace line, the error is -
The type or namespace name 'AddReviews' could not be found (are you missing a using directive or an assembly reference?)

<%@ Import Namespace="AddReviews" %>




Any ideas ?
Dave
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