Working with computer hardware

Question

Ok, I dont even know if Im going to ask this question correctly, but here it goes;
I want to make a program in C# winforms that dials numbers using my internal modem.
I have found my modems DLL file, but Im not sure how to use it. I have no idea what methods, properties, that I can invoke. Im not even sure if Im supposed to use the dll file. Can someone please explain what I should do in the simplest way possible.
Ive also looked for Documentation on the internet about my specific modem, But I havent found anything useful.
I have no experiance with COM INTEROP as well. For some reason I just cant get my head around it. Please advise..
Thanks in advance