Perimeter and area of rectangles
Perimeter is the distance right around the outside; area is the number of unit squares that fill the inside.
A worked example
A rectangle 7 m by 2 m has perimeter 7 + 2 + 7 + 2 = 18 m and area 7 x 2 = 14 m².
The mistake people actually make
Fencing, edging and trim ask for perimeter; covering, painting and turf ask for area. An area answer carries a squared unit.