Seriously @Pioneer1, you wrote that a Republic was "just ONE FORM of an oligarchy." If you would just name two other forms, I think I can help you think about what the terms mean and why saying something like, "A nation can be an Oligarchy, Plutocracy, AND a Republic all at the same time" is like saying a fruit can be an apple, pomegranate, and a kiwi all at the same time.
Just because you can string the words together does not mean that they will make sense. This has nothing to do with college, it is just English.
As an aside, it would also be interesting to read some of the other reasons you are "GLAD" you did not go to college, I'd like to hear other reasons why you are happy to have not gotten an education. Do you feel the same way about a high school education too?