Web App/ Ionic 2 Mobile App - Where to start

Hello everyone,

I am a beginner in Ionic world, so forgive me if my question is too silly.

I want to build a Web Application, but I also want my users to have access from their mobile devices, but as native apps, not PWA.

I would like to have only 1 codebase. A friend suggested using Angular 2 and Ionic 2, but without knowing much to help me, then, that’s why I am here.

So is it possible, to code thinking about a web app and the same code can be converted to native Android and iOS mobile apps?

Should I start first creating the Web App with Angular 2 then Ionic would take care of the mobile apps, or should I start with Ionic straight away?

===Edited===
Let me explain my question better, I would like to know if I build a web app with Angular 2, then I can with Ionic create mobile apps based on that code without much hassle, or should I start everything with Ionic straight away?

I am questioning this approach because the first stage of my project is to deliver a Web App, and only after that the mobile apps.

Any ideas?

Thanks!

Documentation is always a good starting point:

I am in about the same boat as you, but I did a lot of research and choose to learn and go with Ionic.
I checked several comparisons like this -> https://stackshare.io/stackups/xamarin-vs-phonegap-vs-ionic#
and
https://www.codeproject.com/articles/1079101/xamarin-vs-ionic-a-mobile-cross-platform-shootout