What does the role of Iranian supreme leader entail?

Following the death of Ayatollah Ali Khamenei in US-Israeli strikes against Iran, a council of 88 Shiite clerics are set to appoint a new supreme leader. The long-running favourite is the late supreme leader's son, but he faces reservations: the supreme leadership was never supposed to become a family dynasty like the Shahs. But what does the supreme leader actually do?