The automatic detection only works if your printer and your network support auto-discovery. Many networks won't support that feature, and I believe auto-discovery is actually a separate plugin within OctoPrint.
If automatic detection isn't working, you can always enter the IP address manually. If you need help with what port to use, that's already documented on our FAQ page here (OctoPrint uses port 80 like your said):
https://www.simplify3d.com/resources/faq/#quest-6354
The software will automatically prompt you for the API key if one is required, so you don't need to enter that ahead of time.