It's about learning. How the kids learn by interacting with objects. Man, one word: Wikipedia. I did study it, with the original book, but not in English, and many years ago, so I doubt I can help any further than this, xD.
It's the idea that infants are born with a few schemas which gradually become more advanced through their interaction with the world. Children add things to their schemas through assimilation, which is when they see something similar to what they already know which leads to equilibration, and accommodation, which is when they have to change their schemas due to drastic new information because they experience disequilibrium. Equilibration: This is achieved when we adapt to new information by building it into our understanding through assimilation or accommodation. Disequilibrium: An unpleasant feeling that occurs when your current schema is unable to make sense of new information. I hope that helped a little. It's a quite difficult to explain accommodation and assimilation fully. ?
You really need to read your textbooks. You can't expect a proper explanation on something like that through here. It's also quite interesting. Go study it!