Most of this week’s parsha is taken up with a numbering of all the men 20 years or older. Clearly, this was not a complete census. Just a count of those men who would be available to fight in battles.
Each tribe would have a leader. We might think of it as a general. For example, for the tribe of Simon, Shelumiel son of Tzurishaddai was their general, and there were 59,300 fighters.
There was one exception. The tribe of Levi was not counted in this survey of fighters. Instead, their job was to set up the Ohel Moed (Tent of Meeting or Tabernacle) every time they made camp, and to take it down when they were ready to move. They also were to camp near the Ohel Moed.