How would one say "This is a heavy pen"? Meaning, this particular pen is heavy.
What you wrote means "This pen is heavy," because you inserted the definite article before "pen". To write "This is a heavy pen", you need to leave out the def. article and write, هذا قام ثقيل
I don't know! I've been wondering the same. Thinking that it will be revealed in the course, I'm motivated to keep going!