You can create personal waypoints on the map via the website or app, these waypoints will be synced on your account between devices.
In the mobile app you can tap and hold a spot on the map, this will show the "user point" window, where you can get some info on this point, including nearby weather forecast. From here there is an option to save this point as a waypoint.
After populating the add waypoint form the data will be synced to your account. So you can always view your viewpoints on the app map and the website maps.
In the app you can also view a "My Waypoints" list via the main menu "My Wishlist" section.