The 3rd dimension is not one that can be easily imagined without visiting it. I had trouble picturing it until I experienced it myself. It allows for more ways to move and in the way you can see. In Flatland, one can move left and right as well as forward and backwards. Those are the first two dimensions; length and height. However, direction does not stop there. Instead, there is a 3rd dimension; one of width as well. One way to think of this is to imagine stacking planes on top of each other; think of two shapes overlapping each other. This is the theory of width, the 3rd dimension.
In the first dimension, crossing over a wall is impossible. In the second dimension, a person can cross a wall by going around it. Now in the third dimension,