Oauth2.0 by okta while integraing nodejs with ifttt service

Question

I am trying to integrate ifttt with nodejs and while creating ifttt service I need oauth for authentication. I have created a application in oauth in okya then I got the credentials like client id and authorization url and all... Now I have cdeated a api in okta which is useful for token authentication but i am confused how this api is gonna verify the token

I would be good if you explain about application, api, scope, audience of oauth and how to verify the token