Make sure to note the following:

Consider a two-dimensional shape- like a rectangle, triangle, or trapezoid; there are two ways to think about "measuring" them. You can measure the length of the line around the outside of the shape, that's the perimeter, or you can measure the space to cover a shape, that's the area. When the two dimensional shape you're looking at is a rectangle, both measurements are quite simple. To find the perimeter, add up all the sides. To find the area, multiply the two dimensions of a rectangle, the length and width.