A parallelogram is a quadrangle where opposite sides are parallel to each other.
The perimeter ( P ) is the distance around the outside of the parallelogram.
P = 2a + 2b
The height ( h ) is the perpendicular distance from one parallel side to it's opposite side.
Area = b x h
It is important to measure the correct side in this calculation. In the figure, the height is measured from side b to the opposite side b, so the Area is calculated as b x h, not a x h. If the height was measured from a to a, then the Area would be a x h. Convention considers the side the height is perpendicular to is called the 'base' and usually denoted with a b.