You would want to check out the Sutta Pitaka, which records the discourses of the Buddha. It is divided into four main collections, the Digha Nikaya, Majjhima Nikaya, Samyutta Nikaya, and the Anguttara Nikaya. Besides these four main collections, there is a minor collection as well, this is where you will find the Dhammapada.
The Dhammapada is a beautiful text that has much of value; but, it is not the place to find the details of what the Buddha taught systematically explained.
I recommend starting out by looking up the Majjhima Nikaya. Access to Insight has many of the suttas from that collection online, though not every sutta is present.
If you want an actual book to hold in your hands, Bhikkhu Bodhi, an American monk, has done an excellent job translating all four major nikayas into English. The volumes are a little pricey; but, they are worth every penny.