The idea of a flashcard is to write a question on one side, the answer on the other. The student will help to memorise whatever is being set out by the act of preparing the cards. Later a pile of cards is prepared and the questions answered one at a time. If answered correctly the card is moved to one side. If incorrect the card goes to the bottom of the pile. With diligence the pile of repeated cards will soon reduce to nothng.
Examples would be - times tables ~ clock faces for telling the time ~ foreign language vocabulary.
Spelling tests are difficult because we feel strongly that incorrect items should never be shown, but the cards can be used in a similar way if another person reads them out. They only have to be used one-sided that way. Or words and plurals can be used for those "odd" spellings.