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. Go to Downloaded and select the VocabularySpellingCity app. Then select Clear data and Force stop.