How to write an application for the phone?

Question

Mobile development

Good afternoon. The thing is, I’m writing one site, everything seems to be fine, but there is one BUT, you don’t even need a mobile version of the site, but an application that could be downloaded to your phone, register or enter your account and use it, the application must be linked to the site, t .e. to enter your office it was possible both from a computer and from a phone. Something like VK, wildberries, etc. With what tools and knowledge can this be done?
This is the first time I ask this question, so I don’t even know what question to ask Google so that it understands me correctly.

Answer 1

If an application is needed for IOS, applications are written in objective c or swift.
If android is in java or kotlin.
If you want to save time and resources, choose cross-platform solutions (that is, two platforms at once), the strongest players are xamarin forms, react native, flutter.

Answer 2

Google Requests:
PWA
Cordova
React Native
Native Script
Weex

Answer 3

https://flutter.io/