I'm moving this to the 'How do I' section.
Not a stupid question at all. What software are you using?
If you have no real preferences software wise, I'd recommend that you download inskcape (free to use), import your map in that. Make a new layer and use the text tool and start typing away. You can rotate the text, put it on a curve, alter the colours etc. It's by far the easiest way to do it in my experience and it's very easy to edit.