On an iPhone or iPad
It has to be Safari. Chrome and Firefox on iOS cannot install anything, because Apple requires them to use Safari's engine without this part.
- Tap the Share button. It is the square with an arrow coming out of the top, at the bottom of the screen in Safari.
- Scroll the list and choose Add to Home Screen. You may have to scroll a fair way down.
- Tap Add. Then open it from the home screen icon rather than from Safari, from now on.