Mosiah 2:1 - 2:5

Mosiah 2:1 And it came to pass that after Mosiah had done as his father had commanded him, and had made a proclamation throughout all the land, that the people gathered themselves together throughout all the land, that they might go up to the temple to hear the words which king Benjamin should speak unto them.

Mosiah did gather the people around the Temple to hear king Benjamin’s address.

Mosiah 2:2 And there were a great number, even so many that they did not number them; for they had multiplied exceedingly and waxed great in the land.

The crowd was very large and they did not number them.
[It must have been a census that they wanted to take but the time it would take was more than was available.]

Mosiah 2:3 And they also took of the firstlings of their flocks, that they might offer sacrifice and burnt offerings according to the law of Moses;

Anyway the usual animal sacrifices were made at the Temple according to the requirements of the law of Moses.

Mosiah 2:4 And also that they might give thanks to the Lord their God, who had brought them out of the land of Jerusalem, and who had delivered them out of the hands of their enemies, and had appointed just men to be their teachers, and also a just man to be their king, who had established peace in the land of Zarahemla, and who had taught them to keep the commandments of God, that they might rejoice and be filled with love towards God and all men.

The sacrifices were to show their thankfulness for the Lord having saved their ancestors from destruction in Jerusalem and leading them to the promised land. They were thanking the Lord for giving them inspired teachers and leaders that saved them from their enemies in this land. And that they had been encouraged to live the commandments and enjoy the spirit which had filled them with knowledge of who they were in relation to God so they would have a greater regard for their fellow man.

Mosiah 2:5 And it came to pass that when they came up to the temple, they pitched their tents round about, every man according to his family, consisting of his wife, and his sons, and his daughters, and their sons, and their daughters, from the eldest down to the youngest, every family being separate one from another.

As the people gather for general conference, they gathered together in families. The oldest male acting as the head of the family with all his children and grandchildren gathered around him.