Explanation:
Basically the area of sphere is 4πr² where r is radius whose value is distance from centre to the edge of the given sphere whereas π (pi) whose value is 3.14 or 22/7. It is defined as the ratio between circle's circumference and it's diameter. But are you aware about the area of circle?? Actually that is πr². If you notice carefully you'll find that area of sphere is 4 times the area of circle. So, if you're provided with the area of circle you can simply multiply the value with 4 to get the area of sphere. But if not, then simply plugin the value of radius and pi in 4πr² to find out the area of sphere.
But since the formula is almost same then how they're different? Well the difference between a sphere and a circle is because of two-dimensional and three-dimensional shape. A circle is a two-dimensional flat shape figure whereas a sphere is a three-dimensional shape.
Talking about the unit of sphere. The unit we use is always the same as the units of radius i.e. cm or m. Since, it is the square of the radius in the given formula, then the unit is also the square of the units, or cm² or m².