There’s also the original thread about it here which has lots of tips and comments from other people who have used the API:
Most of the examples in that thread are using the OneCall 3.0 API which is documented here:
https://openweathermap.org/api/one-call-3
As noted in the document, you would need to sign-up for an OpenWeather account and wait a few hours for your API Key to become active, then use the URL format @JKB121 showed in his screenshots within an HTTP Action in your rule:
https://api.openweathermap.org/data/3.0/onecall?lat={lat}&lon={lon}&appid={API key}
I would also note that you might find it easier to Download the large screenshots by tapping the link below the image after opening the image preview:
Edit: Oh, and there’s also a neat thread about using Chat GPT along with the aforementioned weather API to get some neat AI generated summaries: Open Weather API (and Chat GPT)