On iPhone / iPad

1. Make sure you are in Safari (Chrome on iOS cannot install)
2. Tap the Share button — the square with an arrow
3. Scroll down and tap Add to Home Screen
4. Tap Add

On Android (Chrome)

1. Tap the ⋮ menu, top right
2. Tap Add to Home screen, or Install app
3. Confirm

Not seeing it? Some browsers (Firefox, Brave, Samsung Internet, any in-app browser) hide or rename this. Chrome is the reliable one.