The 12 tribes of Israel are named after Jacob‘s 12 sons. They are (in order of age) Reuben, Simeon, Levi, Judah, Dan, Naphtali, Gad, Asher, Issachar, Zebulun, Joseph and Benjamin. Leah gave birth to Reuben, Simeon, Levi, Judah, Issachar, and Zebulun. Rachel gave birth to Joseph and Benjamin. Leah’s maid, Zilpah, had Gad and Asher, and Rachel’s maid, Bilhah, had Dan and Naphtali.
Israelites all descended from these 12 brothers, and maintained the identity of their tribe. Following the Exodus, according to the Torah, descendants of Joseph were known as descendants of one of his two sons, Ephraim and Menashe. This made for a total of 13 tribes. Some from the tribe of Levi became the priestly family, known as Kohanim.
