Perimeter is the space around a two-dimensional shape.
For rectangles, the formula is: Perimeter = length + width + length + width P = l + w + l + w OR P = 2l + 2w
For squares, the formula is: Perimeter = 4 x lengths of the sides P = 4s
Area
Area is the space inside a two-dimensional shape.
For rectangles, the formula is: Area = length x width A = l x w
Volume
Volume is the space inside a three-dimensional shape.
For rectangular prisms, the formula is: Volume = length x width x height V = l x w x h
Which one is it?
When trying to decide if a problem is looking for perimeter, area, or volume, draw a picture of the word problem to help you visualize it. Consider if the shape it's describing is 2D or 3D, and whether you are looking for the space inside or outside the shape.