Payment Gateway API Integration

Hi, I am trying to integrate Payumoney payment gateway in my app. I haven’t started building the app yet, since I am a total beginner to API. I have been trying to learn more about API and how to get data using web component. But in most of the tutorials I have seen, the process is relatively simple, using an API key and getting data using a URL. However, when I looked at Payumoney API Docs, it uses cURL. So I tried to learn more about cURL, came to know that it is a command line tool. I am trying to create an app where users select some products and checkout, and pays uses payumoney gateway. Even if I use cURL, how can I display Payumoney payment page? I am really confused about all these. Can anyone please get me started on the right direction? (Please don’t point to youtube tutorials about payment gateways, all I have seen just shows the app working then tells to pay for aia file.)