Reddit reviews A Nietzsche Compendium (Barnes & Noble Library of Essential Reading): Beyond Good and Evil, On the Genealogy of Morals, Twilight of the Idols, The Antichrist, and Ecce Homo

I wouldn't worry too much right now about knowing everything perfectly; you're still finding your foundations and areas of interests. Sophie's World is sorta where I started too, and I'd recommend maybe going back and seeing if there are any philosophers that you found particularly interesting. That would be one way to start.

If you want to go deeper into general philosophy, Bertrand Russell's History of Western Philosophy is like a much (much much much) denser and more intense version of Sophie's World. If you're not sure where to go next, this will give you a much more in-depth view of even more philosophers (although he skips Kierkegaard, which is my main gripe with the book, but oh well, still would recommend it). One thing I personally loves about this book though was how he connected philosophy to history, art, science, poetry, and so many other fields. It's really made me want to switch my major to...Everything! Philosophy's still at my core, but this book really got me interested in other fields as well.

To go further in recommendation, Plato's dialogues are generally considered to be pretty important to a foundation of philosophical understanding. The Apology is a pretty easy one; it's less of a philosophical text in the traditional sense and more a sort of kick-off for the field, where Socrates explains why philosophy is important, and why he pursues it. The Republic is also pretty important for understanding Plato's political ideas. All his dialogues, though, are generally pretty good reading, and I'd recommend reading some.

To go past that, Aristotle's often a good read, primarily his Nichomachean Ethics is a pretty good introduction to his philosophy, much of which is a response to Plato.

To move onto modern philosophy, it tends to get a bit more technical and tricky, but a great and very easy-to-read modern philosopher is Descartes. I'd recommend Meditations on First Philosophy and Discourse on Method in Discerning Truth in the Sciences as good introductions to modern philosophy, which tends to focus on slightly more technical forms of logic, rather than conclusions drawn from more vague observations.

(NOTE: found a book that combines both the Descartes writing mentions into one here).

Another important thinker who might not be hard to understand but who will definitely shake you is Nietzsche. This documentary is a pretty good introduction to him, but if you want more, I'd recommend this collection as a good overview of his philosophy. His works are quick reads, but they will stick with you, and I consider him to be one of the most important thinkers to understand the modern age.

Eventually though, you'll need to start taking on more challenging texts. Hopefully though, you'll be well informed enough by that time to have found a niche that you personally are interested in, which will make it much more interesting and fun! Never hesitate to come here with questions. Good luck!

I started my interest in philosophy with Nietzsche when I found Zarathustra in a bookstore. As others have said, it's not a good place to start. I then read all these, and also read some of The Gay Science as well as some of Kaufmann's book which is a good starting place, although I personally found Heidegger's lectures on him more interesting and insightful (although much more biased and with a more explicit agenda).

Personally, I don't know if there's really the place to start with Nietzsche, because he doesn't have a single system in the traditional sense. While he offers hints at a system, and while there are certainly thematic threads that run throughout his thought, there's not a single text where he outlines a single system. He came close in The Will to Power, but never finished it, so we're left with his notebooks and outlines, still aphoristic. It might be worth thinking about why you want to read Nietzsche; his thought covers so much territory, and in such odd ways, it might be helpful to have a "way in" or angle with which to read him. This is why I liked Heidegger's lectures, and am admittedly wary of Kaufmann's book; I'm just not sure a single unified Nietzsche is out there, but he's a fascinating sower of seeds. Whether it's history, art, religion, culture or some combination of all those fields, he's got a lot of interesting things to say, but I'm not sure there's a single place to start, given the lack of a single kernel of thought. This is obviously largely my opinion, but I thought it was worth noting.