Drawing just one card is the easiest and probably the most common method of reading. Without a storyline like when interpreting a spread, there are no cards to compare and contrast. Simply interpret the card as the answer to the question.
Alternatively, this method may be used repeatedly in succession to allow the cards to tell a story.
Shallow, not deep. Something is new, perhaps it is information, an idea, or a message from your inner voice. The Letter indicates that you may receive news soon, but you have to open it before you'll know if it's good news or bad news.