iPhone Safari: tap Share, then Add to Home Screen. Open the new icon while still online and download the offline pack inside the installed app.
Android Chrome: use the Install app button above or the browser menu, then launch from the new icon.
Your walk is remembered: progress, last route position, trip distance and breadcrumb track are saved only on this device and restored when you reopen the app.
Important: location and compass permissions must be granted from the Start navigation button. Test outdoors before relying on them.