Using outlook rest notifications api

I created a function in azure functions that is triggered by http request. Also I have a web app that used for clients to subscribe to my app. My app and web app is written in .net. My goal is to set a subscription button in the web app, so when the user subscribe it would allow me to get push notifications about new mail in his outlook inbox folder and send http requests to my azure function that includes the content of the newly received mail. I read the doc about this API but couldnt understand it and what should I do to get my goal. Also I didn't find any examples for this. How can I achieve my goal?