American government is broken up into different levels. You have your top level, the Federal government, who makes and enforces national laws; there's the state government, who makes and enforces state level laws; then there's the local level, who makes laws pertaining to specific cities or neighborhoods.

A Senator is part of the federal government. They get elected by citizens of a state and are supposed to go to DC to represent that state in the national government. They make sure that people like us get a voice. An example would be a senator from Kentucky representing a district with a lot of coal miners, so they are pro-fossil fuels. A senator from LA would be trying to pass clean air bills because the people that elected them deal with a lot of pollution. These two senators probably will be on different sides of the fence on multiple core issues, but they are supposed to help one another see a different perspective and come together to find a solution that makes everyone happy.

The governor is kind of like that states president. They do similar things: passing bills into law, activating the military (Governor's have the power to activate their states national guard), and managing the executive branch of government.

A mayor is kind of the "president" of a city or town, but what they do depends on the city structure. There's a few different roles a mayor could serve, but for the most part people look to them as the leader of a city.

This is a super simple answer, but it's solid foundational knowledge and gives you enough to work with to know what to Google if I didn't go in depth enough.

Please nobody try to "aCkSHuAllY" me in the comments. Lol