Read, read, read. If ou wanna learn about philosophy, read philosophers, it's that simple.

Plato, Aristotle, Socrates, Hume, Locke, Bentham, Voltaire, Kant, Schlegel, Hegel, Kant, Spinoza, Nietsche..... There are many more, but the key to philosophy is reading. And not just philosphers, but also other literature of the same period, for example, you'll get so much more out of German philosophy if you read Goethe, Nietsche writes about Greek Tragedy, etc. etc.