When you're in online mode (see User Guide here how to switch between online/offline mode) all the downloaded map tiles will be saved to your phone's memory. So you can turn online mode on and move around on the area you want to get saved for offline use. There's also a feature (the lowest icon on the menu on the left side) that allows you to download all the map tiles from the selected area and from the selected layers, but that might not work in the 4.2.0 version.