State legislatures create laws for their respective states, check the power of their state governors and reserve the power to ratify amendments to the U.S. Constitution. The laws that state legislatures create often deal with crime and contracts like marriage. State legislatures also participate in carrying out federal programs within their state boundaries.
State legislatures make the laws that govern the states. Unlike the U.S. Congress, which deals with issues like foreign policy and national security, the state legislatures handle more of the issues that affect constituents in their day-to-day lives: marriage and family law, wills and estates, penal law and state infrastructure. The state legislatures establish the state budget; the way in which the government allocates money during a fiscal year. This creates a layer of overlap with the federal government because the state legislature decides how to fund federal programs.
A state legislature checks its governor in much the same way the U.S. Congress checks the president. It can override vetoes, impeach government officials and amend the state constitution.
State legislatures also posses the important power of enabling amendments to the U.S. Constitution. According to Article V of the Constitution, the state legislatures can apply to Congress for a national convention to propose constitutional amendments and then ratify the proposed amendments.