I had a T-Shirt company back in the mid-90's...learned to make logos and stuff with CorelDraw. Got into the 'net very soon after that and web design, in particular, around '98.
Never took a course...learned as I went. Just like any software, click it and see what it does
How do you learn good design? Poke around and study what works (converts). Then mold what you see in your head with what works.