What is the main purpose of state legislatures?

Each state in the U.S. has a state legislature. The state legislatures main purpose is to make and pass laws at the state level.

An integral part to each state government - indeed where the people of each state are best represented - is the state legislature.

State legislatures are the respective representative bodies for the people of each state.
The primary responsibility of any state legislature is to design, draft, and vote on bills and laws to govern each state. Bills and laws generally go through several committees prior to being voted on in the entire assembly, through which the bills and laws are changed, amended, or killed altogether.