A cube's surface is made of 6 squares, (you can count it there are 6 faces :) ). A square's surface area is [tex]{ x }^{ 2 }[/tex] x is length of one edge. So we will multiply [tex]{ x }^{ 2 }[/tex] by 6 to find the total surface area. The x is given 8, let's plug it in the formula.
[tex]6{ x }^{ 2 }\\ \\ 6\cdot { 8 }^{ 2 }=6\cdot 64=384\quad square\quad units[/tex]
Answer is C