Political science is a branch of social science. Anything that has to do with the study of politics and government falls into this discipline.
For the most part, you can split political science into two branches – the first one that deals with governments, political representatives, policy making, political functions, and other official events.
The second is the one that examines how people interact with governments, such as how those political representatives are chosen, and how people influence and respond to politics in their city, state/province, and country.
It is an extremely broad field because anything that is associated with politics can fall under political science. If you are examining the relationship between two different countries, that is international political science.
If you are talking about how the laws passed by a current group of state senators influences how people can vote in the next election, that is local or state level politics. There are many different examples of different types of political science, all of which fall under the area of political science.