On desktop, you can add and remove favorite stations by clicking the star icon while browsing stations or via a station’s page by clicking the Favorite button.
On mobile, you can add and remove favorites by tapping the heart icon. You can press on the more menu on the station page, and tap "Remove From My favorites." You can also remove and reorder your favorites in Settings > Manage Favorites.
There’s no limit to the number of stations you can favorite.