How Do You Explain A Cross Section?

Answer 1

-- Take a solid object that you can hold in your two hands.

-- Put it down on the table. Hold it firmly with one hand so that it doesn't move.

-- With your other hand, take a big sharp knife, cut the object all the way through, into two pieces.

-- Put down the knife. Pick up one of the two pieces. Turn it and look at the new flat side that it has,
since it got cut.

That new flat side that it has now is a "cross section" of the original object.

It doesn't matter which piece you pick up. The new flat sides on both pieces are exactly the same size and shape.
(Although they are the mirror-images of each other.)