The meaning of the rundll32 command

Question

rundll32 url.dll,FileProtocolHandler https://bsu.by

What does each word mean and why does it eventually open this link in the default browser?

Answer 1

It's a rather old utility that loads a DLL (with LoadLibrary), finds an exported function (GetProcAddress), makes its best guess about the expected parameter types from the looks of its command line, and invokes said function. In this case, since there's one parameter and it's not a number, rundll would assume - a single string (LPCWSTR).