The Sun is the happiest card in the Major Arcana. This card means that there is happiness, good fortune, harmony, success, and joy on the way or happening right now. It is the card that represents that the universe is coming together for you and it is supporting your path which means you are going to achieve what you have been after. In fact, you are about to go on to something even greater and become successful.
This is a card that also represents vitality, marriage, giving birth, enlightenment, and financial success. You have been going through a period of confusion which was shown by the Moon, but the Sun is now shining giving you the hope that you have been praying for. The Sun can represent any happy and successful occasion. One example is that the Sun comes up when you are going to get that promotion at work that you have earned. This is something you have been looking forward to and you are finally getting it. This is a time of feeling accomplished as well as a time of happiness.
Going back to the high schooler example, he aced a difficult math exam. He is ecstatic and he feels great and wants to celebrate as a result. He may also be ecstatic because a girl that he likes is interested in dating him. Those things are represented by the Sun.
When the Sun comes in reverse, it is indicative of low vitality, impressions that are false, lack clarity, disappointment, and sadness. Something that appeared promising turned out to be disappointing.
Astrologically, the Sun is tied to its own planet, and it is the 19th card in the Major Arcana.