Are we walking around the outside, or covering every blade of grass?
Walk round the edge and you measure the perimeter: add up every side, in metres (m).
Cover every blade of grass and you measure the area: the squares inside, in square metres (m²).
Every shape is a pitch, or part of one, drawn to scale on a grid. A side with no label can be found from the drawing: compare it with the opposite sides.
Pick a stage
Each stage: a worked example, then 10 questions, easiest first.