How to get Indian railway api

I want to create an app.rail way tickit booking app.how can I do that ?

Use google to do a good amount of research on that very specific topic. Or go to that specific api’s site / console and do exactly what it tells you to do.

Or pay someone to build that app for you, or to provide chunks of code that will get you far enough to finish on your own. Upwork.com has plenty of available freelancers who will accomplish those things for you, in exchange for currency.

You may also want to rethink your strategy. Think of it this way. Anyone who could answer your question with some level of expertise, won’t. They put a ton of work into being in a position to be able to answer it.
Anyone who does answer your question won’t have the expertise to provide an answer of any quality whatsoever.

By taking their advice, you’d end up with an app that books tickets for horse and buggy rides out of Manhattan instead of booking tickets for any railway, anywhere.