Where do I start? ???
Read and understand the user stories expected. Look at the demo to see site functionality. Look at what other campers have done for inspiration.
Draw out how you would like your weather app to look and decide on what features it should have. Next, try to create a basic HTML skeleton that will be your design and use CSS to make it look like you originally planned on paper.
Then, try to write out in plain language how these features will work (as inputs and outputs). You could use flowcharts to map out the user interaction between the UI (User Interface) showing what would be moused over, clicked, orentered and what would happen based on that mouseover, click, or input.
Once you have all of this mapped out, then you start thinking about how you want to store any data to be used throughout the api. What data structure(s) will you use?
You could think of each UI interaction and response as separate piece of a larger puzzle you need to eventually put together as a whole. At this point, you can start writing your algorithm/steps for how each piece should work.
I saw a pretty good tutorial at https://www.youtube.com/watch?v=eLK28VPJvCE&list=PLHdCowjFIBmLRvwkK0UNz0OA10pYI4H0g
I used this to get the basics, here is one thing you want to do. Instead of using the api he is using, just replace it with this api --> https://fcc-weather-api.glitch.me/
Its just accessing a object and calling the api, something he shows in the first couple videos of the series.
The outputs of the apis are kinda different, so accessing the two objects output will vary.