It's fairly simple on modern Android. You simply download the APK file, and open it. It will then walk you through the install process.
If you haven't installed an app from your web browser before, you'll get a prompt saying your security settings don't allow the browser to install apps. There will be a settings link there. Tap that link and you'll get a list of apps that have the capability to install things. Find your web browser in the list and tap the toggle to give it permission, then back out. Then your app will install.
And these people wonder why their kids leave as soon as they are legally and/or financially able to.
Sooner, in some cases.