I'm trying to make an VB.NET application that allow user to type in username + password then log in to a server that use oauth authorization. But I don't know much about oauth, so I really need your helps!
Why not try a library with some documentation? I did a quick search and found this page with a link to 3 .NET libraries for OAuth, and the first one I clicked had extensive documentation.
You don't need the code to be in VB to use a DLL. And C# and VB .NET are close enough in syntax you ought to be able to figure out 90% of it from looking at a C# example. The 10% you don't get is what we'd be glad to answer. Give it a look, get something almost functional, and we'll give you that last push.