To govern the people...

Aside from an innate sense of "right" and "wrong" there is another sense that we humans have an opinion on naturally (it also has to do with ethics as well). When defining the boundaries and definitions of any other branch of philosophy is an appropriate starting point, when it comes to political philosophy we should start with is most base question and go from there:

(i) What sort of laws and/or governmental structure (if any) is/are the most appropriate for our community (and for the communities of others for that matter)?

Political philosophy is, to be honest, not my favorite branch of philosophy, but it is one that everyone has an opinion on and to be fair, a very important one. While making conjectures about ethics or metaphysics or logic or epistemology political philosophers are often commenting on the current practices in government. Anyone who has an opinion about (i) is a political philosopher. This is where political philosophy becomes diverse, because there are so VERY MANY ANSWERS to (i).

There are a multitude of types of government. Each of these types of government all have variations, and those variations have their own variations, and so on. Indeed, even the absence of government has variations because the absence of government is itself a political philosophy.
The best way to attack political philosophy is to start with the type of government you are most interested in studying and jump down that rabbit hole; there will be ample reading to follow.