How does the AlphaZero chess playing computer evaluate positions?

From what I have read, the computer was only taught the rules of the game. See, for example, this aricle It shows an illustration of neural network. What I want to know is, what information is stored? It can’t just be the location of pieces on the board, because it will probably never again encounter the same board position. Does it count the number of pieces taken? Does it have some other way of evaluating a given position, and how is that possible if it was only told the rules of the game?