Choose the right page
In your web browser, you should go to the page you want to start on - probably main page of the site, although you might want to jump straight to your account or the advice centre. There should be an option called Add to Home Screen on most mobile devices.
Android phones and tablets
On Android devices the menu is three dotted lines (usually at the top right of the screen, although on Samsung phones it might be at the bottom).
If you don't see the bar with the three dots (menu button) on it, scroll down the page, then quickly scroll back to the top and the bar should appear.
This menu should have the Add to Home screen option.
iOS (iPhones and iPads)
On current iOS devices (iPhones and iPads) you need to click on the icon that brings up the sharing menu, which looks like a square with an arrow coming out of it.
Near to options like Add to bookmarks and Add to favourites is the Add to Home Screen option.