Area is always given in square units. Surface area is just a type of area where you look at the sides of a surface. To see why area is give in square units, look at the square. If you have a square that is 2 inches in every dicrection, you find it area by multiply the height by the length. This is 2ftx2ft. The 2x2 becomes 4 and the ftxft becomes square feet. The idea is similar for any area.
square units
units squared
It is the area and is measured in square units.
You can put an infinite number of square units on any surface if the unit is infinitely small
The surface area of the square: 5.5*5.5 = 30.25 square units