Reddit reviews Cognitive Neuroscience: The Biology of the Mind

• Purves text isn't that easy but a great and thorough introduction.
  
• Gazzaniga's text is fantastic but less on the biology side of things.
  
• Others have mentioned Kandel's text but I don't think that's a good first text for anyone wanting to "dip their toes" in.
  
• Someone else also mentioned the Bear text, which is very good.
  
  Those are really all you'll need; from there you will find things on your own or from professors.

Cognitive Neuroscience, by Michael Gazzaniga

Two things, (1) I'm going to recommend mostly books and not textbooks, since you're going to read plenty of those in the future. And (2) I'm going to only focus on the area of cognitive psychology & neuroscience. With that being said:

Beginner:

The Man Who Mistook His Wife for A Hat: And Other Clinical Tales By Oliver Sacks

Brain Bugs: How the Brain's Flaws Shape Our Lives By Dean Buonomano

Kludge: The Haphazard Evolution of the Mind By Gary Marcus

The Trouble with Testosterone: And Other Essays on the Biology of the Human Predicament By Robert M. Sapolsky

The Seven Sins of Memory: How the Mind Forgets and Remembers By Daniel L. Schacter

Intermediate: (I'm going to throw this in here, because reading the beginner texts will not allow you to really follow the advanced texts.)

Cognitive Neuroscience: The Biology of the Mind By Michael S. Gazzaniga, Richard B. Ivry & George R. Mangun

Advanced:

The Prefrontal Cortex By Joaquin Fuster

The Dream Drugstore: Chemically Altered States of Consciousness By J. Allan Hobson

The Oxford Handbook of Thinking and Reasoning By Keith J. Holyoak & Robert G. Morrison

Principles of Neuroscience is a grad-school level book. I would not recommend shelling out $100 for it.

This book, Cognitive Neuroscience by Michael Gazzaniga, is a great book for someone at your age. It's super cheap and very easy to understand.

If you go with a textbook from an author like Kandel or Purves or Bear, you are going to be jumping straight into the deep end and might easily get discouraged.