By definition a Paleo (short for Paleolithic) diet entails eating the same foods that our hunter-gatherer ancestors did.
If you can imagine that there were suddenly no stores *gasps* , and your survival depended on what you could catch (animals), or pick (fruits and vegetables) *I would die a slow death*, then you will be close to understanding the basics of the diet.
Check out the neat infographic below for a quick run down of the Paleo Diet.
It's really not that hard to grasp, but maybe a little harder to actually do consistently in the beginning.
Eat nothing "man-made". Also no grains, dairy, legumes, and try to eat only organic and local if possible, or things you've grown/raised yourself. Pesticides are most definitely "man-made", and one of the biggest causes of disease today.
If you've never tried eating the Paleo way before, I can't think of a better time to try it out.
You never know, you may have just stumbled on to your new approach to eating!