In the Search Mode, you will be able to form as many words as you want using the given letters, but the game will choose certain words that you will have to spell in order to complete the level.
You will have to spell your words in the game area, where you will see the letters assigned for the level you are at. Although the objective of this game mode is to spell the words that the game determined as necessary to complete the level, you can also spell other words that will help you complete the bonus bar, which will give you a clue as soon as you complete it. The longer these words are, the faster the bar will fill for you to receive the bonus.
Once you find the necessary words for the level, you will have completed it and move on to the next.