How do you get area of an object?

It's the length times the width times the height.

No that is the volume!

The surface area of a three dimensional object is easy to calculate if it has rectangular surfaces (like a cube) and slightly more complicated if it does not but is a regular solid (like a tetrahedron or dodecahedron) (one with all the sides the same size)

Any irregular two dimensional object can be broken up into tiny squares and the area of each and every square added together.