This artice will mention how to create and expose APIs.
First, you need to create a backend flow. If you don't know how to create a backend flow, you can check the artice
Then, select 'Webhook' trigger and add your action nodes and in last action node, return your data that you want to return from your API.
Also you can change your url of API from Url input in Parameters.
That's it. You can copy the link of API from 'Copy webhook url' button as you see the ımage above and use it.