Its own window, its own icon, no address bar.
It is the same MyAccount as in the browser, but in its own window with its own icon in the Start menu or in the Dock. Nothing is downloaded and installed in the usual sense, so it takes up a few hundred kilobytes and updates itself. You log in once.
Click the install icon at the far right of the address bar, it looks like a screen with an arrow. If it is not there: the ⋮ menu at the top right, then Cast, save and share and Install page as app. In Edge it is called Apps and Install this site as an app.
Open the page in Safari, tap the share icon at the bottom and choose Add to Home Screen. Other browsers on iOS cannot install apps, that is a limitation in iOS and not in the site.
Chrome usually suggests the installation by itself. Otherwise: the ⋮ menu and Install app or Add to Home screen.
Firefox has no installation for desktop computers. The site works just as well in a normal window, you just get the address bar thrown in.
⋮ inside the app window.