OnSong is designed to store your library on your device. This allows you to access your songs anywhere you go without the need for an Internet connection. This means if you have multiple devices like an iPad and an iPhone, they both will have separate libraries.
OnSong provides the ability to synchronize your library between devices using a cloud-based storage service like Dropbox. For more details, open the Songs Menu and tap on the + button on the bottom right to view the Add Songs screen. Choose a storage method under the Synchronize section in the list.