Hey there!. Good luck with your first project.
If you have problems doing overworld stuff I'd recommend to ask in SMW Hacking Help
forum. This forum is dedicated to give some snippets or showing off the progress of your current projects.
Quick answer to your question. Make sure to add paths (green paths, or blue paths if the player is in water), and also make sure in your first levels in main world or subworlds (yellow/red dots, castles, ghost houses, etc), have enabled the desired direction.