On the 24th of Summer you can attend the fireworks display that is visible from Mineral Beach. At 6:00pm head to the beach to meet up with the rest of the Mineral Town villagers. After talking with everyone on the beach, the fireworks will begin. When it's all over you'll reappear back in your farm house and it will be the next morning, so make sure you've finished all of your farm work before you leave for the beach.
When you have a boy that has at least a green-colored heart, he can be invited to watch the fireworks with you. Just talk to him and ask if he would watch the festivities. If he accepts the two of you will move to the end of the dock for a better view.
You will earn 1 Event point the first time you participate. Inviting one of the bachelors to watch with you will raise his affection level.