Paste the API Key you just copied in the text box on top of the page, and click on Explore API Responses.
On the right hand side you can see what the specific API does. Click on the API you’d like to use, and it will expand. For some of these you will need to enter a device ID. Click on the second one to fetch all devices for an account and click on Try it out! You will see all your devices listed with a device ID, use this ID in the remaining to get your data.