In the last 24 years it has all been BasicVM and Mumps. Just set variable names and go. The Dim statement in Attachmate Enterprise Basic is the closest. Mumps uses a call to outside programs, but they don't have to be declared, just present to run.
I have heard of declarations to outside programs, and understand conceptually, but never had to write one that I recall. I don't know how it's done in Windows, or what it needs to contain.
I also do better "figuring out" when I have some kind of starting point. I'm not good at starting from nothing and getting somewhere.