I’m not using the binding so it’s difficult to answer some questions, but I did find some info that will get you started.
Here are the documents for the binding and some examples for creating things, items, and sitemap. https://github.com/cweitkamp/smarthome/blob/c9cc52125c66370664ab82ddb366b65628aff0d8/extensions/binding/org.eclipse.smarthome.binding.openweathermap/README.md
Here’s a topic for the binding I found here on the forum that may be helpful.
https://community.openhab.org/t/announcing-openweathermap-binding-for-eclipse-smarthome-openhab/46420