In order to completely close the program on an iPad, you will need to double-click the home button at the bottom of your iPad, then swipe upward from the bottom to close the VocabularySpellingCity app. For older models, double-clicking the home button may display open apps in a toolbar along the bottom of the screen. Press and hold the VocabularySpellingCity app icon until it vibrates, then click the "-" sign to close the app.
In order to completely close the app, you will need to go into your Settings and select Apps or Application Manager. Select Downloaded and then select the VocabularySpellingCity app. Select Clear Data and Force Stop.
In order to completely close the program on a Kindle, you will need to swipe downward from the top to bring up your Settings menu. From Settings, select Applications, then Manage All Applications. Select the VocabularySpellingCity app, then select Clear Data and Force Stop the app.