Philosophy is a very broad topic. You can spend a whole life time studying philosophy and not even come close to exhausting it. For example, there is ancient philosophy, modern philosophy, philosophy of language, epistemology and the list goes on. Moreover, philosophy is usually very difficult to read. In light of all these points, I would suggest the following.
First, narrow down what you want to study in philosophy. After you do this, go to the search box on enotes and type in philosophy. If you want to study something more specific, then put in that author or work in the search box and lots of resources will come out.
Second, after you have done this, and you want to go deeper in the study of philosophy, then work through the bibliography that enotes and other books give. In this way, you will start getting into the secondary sources and scholarly opinions.