Area is the amount of space inside a plane figure, measured in square units. To find the area of a shape, we multiply its length by its width.

For example, let's say we have a square that's 3 units wide and 3 units tall. To find the area, we multiply 3 x 3 = 9 square units. So, the area of the square is 9 square units.

Here are some formulas and examples for other basic plane figures:

Triangle: Area = 1/2 x base x height; Perimeter = sum of all three sides For example, a triangle with a base of 4 units and a height of 3 units has an area of 1/2 x 4 x 3 = 6 square units, and a perimeter of the sum of its three sides, which depends on the lengths of each side.

Circle: Area = pi x radius squared; Circumference = 2 x pi x radius (or pi x diameter) For example, a circle with a radius of 2 units has an area of pi x 2^2 = 12.56 square units, and a circumference of 2 x pi x 2 = 12.57 units (rounded).

Square: Area = length x width; Perimeter = 4 x length (or 4 x width) For example, a square with sides of 5 units has an area of 5 x 5 = 25 square units, and a perimeter of 4 x 5 = 20 units.

Rectangle: Area = length x width; Perimeter = 2 x length + 2 x width For example, a rectangle with a length of 8 units and a width of 3 units has an area of 8 x 3 = 24 square units, and a perimeter of 2 x 8 + 2 x 3 = 22 units.

So, that's how we calculate the perimeter and area of some basic plane figures!