Shavua Tov. Tonight is Lag B'Omer which is a happy day in the Jewish calendar. It is the day that the plague that killed 24,000 students of Rabbi Akiva ended.
It is also the Yahrtzeit of Rabbi Shimon Bar Yochai, who authored the Zohar, the main book of Kabbalah. It was his wish that this day be one of celebration and joy. The bonfires were to be viewed as Yahrtzeit candles for Rabbi Shimon Bar Yochai.
It was also a custom to go out with bows and arrows on this day. The word for bow and the word for rainbow is the same, קשת. Because of Rabbi Shimon's holiness, there was never a rainbow in his lifetime. Hashem never had to consider destroying the world because Rabbi Shimon was in the world. Therefore, on Lag B'Omer there began the custom of bows and arrows.
The count for ספירה is obvious.