You can read about the API integration related information and request access in FYERS API Documentation. You are required to create App here and it shall be approved in 1 working day after you fill the required form therein.
Where can I read the Terms and Conditions for API usage?
Can I place BO/CO through FYERS API?
Can I place Basket Orders through FYERS API?
Does FYERS provide any support in setting up my Trading System or Algorithm for Individuals?
Does FYERS provide free trial access to APIs for developers?
Do I need to pay for Datafeeds?