You can either build true native apps compiled in swift or java that run on iOS or Android;

Or, you can use something like react-native that runs a webapp version of an app designed to look like a native app.

You can also just send your users to your mobile optimized website that has app like functionality and not worry about making them install something to their phones.

To understand mobile apps start with the case of just a website like www.fedex.com and you happen to open that website on your phone vs. your computer. You might call that a mobile app because you are using fedex's webapp on your mobile device. But you are doing it in your phones browser just like on your computer you use chrome or firefox, or safari.

But you can also goto the app store and download the fedex app. That would be a possibly native app. I say possibly because the app you download from the app store or playstore might just be a browser called a webview that has no address bar. That it you are still running a webapp in a browser even though you install it from the app store. But the browser is hidden from view. The install process gives you the illusion you are running a native app.

What is a truly native app then? It has no hidden browser. The app might still have buttons and things you touch and interact with but they are NOT the same technology as your desktop web-app. Specfically they are not html, css and javascript doing all the complicated things that can be done in a browser. See a web browser is some of the most complicated code ever writen. Taking HTML and making it render the design perfectly, on any computer, on any operating system, windows, mac, etc. It wasn't easy. The browser wars of the 1990s and 2000s gave us these amazing tools.

But before browsers we used to use alot of native desktop apps too! If you remember before google docs, sheets, etc. we have microsoft word, excel. It took a long time before browers could run something like excel inside them.

Phones have some very specific hardware and features that still make running truly native code, (i.e. word and excel) a lot better than trying to get the code to work in just a browser.

So if truly native apps are not using html, css and javascript what do they use? They use a language called Swift for iOS Apple apps and Kotlin/Java for Android. Within the languages are frameworks for doing what html/css did. You have to build your app like any installed based app on the operating system.

So how do you know what you want to build for your mobile app? Which direction do you pick between: 1. Just a web-app, 2. A web-app wrapped in a browser you install 3. A truly native app. It depends. Some business start as truly native, installed apps only without even a website! If your app needs certain features of the phone like the camera, and bluetooth, and location, etc. And if you need that polish that makes your app really stand out and look perfect, then truly native is what you need.

But maybe you already have a nice webapp and it just needs a few fixes to run well on a mobile device. Well then you could release that as an app running with a browser on mobile and save yourself all the development effort of writting the native apps without html, css and javascript.

Or maybe you are just starting the business and need installed based apps but they don't need that perfect polish, and won't need to use the camera, or bluetooth etc. If you are ok with your apps running browser code only, then you can use something like react-native and write your logic with browser tech and also never incur the cost of Kotlin/Java and Swift.