Let me give you a simple version, hope it helps
It's very simple. Duality is the idea that there is two. You, being separate from others. A separate self and an outside world. Non-duality means "not two". When you have a dream at night, and you wake up you realize that everyone in your dream was actually just a part of your own consciousness, not actually a separate person from you. Well, that's non-duality in a nutshell. We're all part of the same indivisible field of consciousness. The world and all experiences within you. You, are consciousness. What can appear as many drops of water, forming many different streams, is all connected together into one. The flower and the bee, are completely inseparable. The earth and you are not separate. Your neighbour is part of you. All the people are in you. The dog is in you. The cat is in you. The plastic bag floating in the breeze is in you.