C# .Net interface testing tools

Sorry for the noob question,

I am responsible for testing of a software interface created with C#.Net tech, consists of a lot of text fields and financial restrictions. Since because I don't have any experience on software testing area, I don't know how to begin with. I am looking for an automatic testing tool you might suggest.

Let's say I want to test the calculation of a transaction. I have an interface to create a fee for transactions, and an algorithm to calculate how much the fee will be. The fee must be calculated on various kinds of elements. (Like the amount of the transaction itself, etc.)

Let's say I want to test that this algorithm works. What I usually do is to create a lot of different scenarios, test them one by one.

Is there any tools do this kind of jobs automatically?