A flashcard is a piece of paper (preferably a card stock paper like a 3x5 card) with a word or concept on one side and the translation or meaning on the other side.
To make Spanish vocabulary flash cards, write the Spanish word on one side and the English word on the other (or better yet, a picture of the meaning of the Spanish word.)
How to study with flashcards:
Place the cards in a stack so all the Spanish words are facing the same direction.
Pick up one card and read the Spanish and say the English word OUT LOUD Check the English side to see if you were right.
If you translated the card well, put it in a 'I know it' pile. If you didn't translate the word correctly, put it in a 'I don't know it' pile.
Continue through the stack, adding to your 'I know it' or "I don't know it' piles.
When you have gone through all the cards, pick up the 'I don't know it' pile and go through them, saying OUT LOUD the Spanish word with the English translation.
Repeat step 2 and 3 with the 'I don't know it' pile, placing any cards you now can translate correctly into the 'I know it' pile.
Repeat step 5 and 7 until you have all the cards in the 'I know it' pile.