What is the length of each side of a square that has an area of 9 units²?

Consider a square, whose diagonal measured d units
Area of Square =d&1\2.the area of this square can be calculated using the formula Area=d2\2.
let us consider a square whose sides measures a units.
the side being a here, we have Area=a^2
measure diagonal be d units.Diagonal divides the square into 2 right triangles.
And so 9^2 is 81 or it maybe 18 since it's using length so add  and then ,multiply since it's also using area so then, 9^2 and 9^2 and 9^2 you'll find your answer by  ADDING 9 UNITS AND THEN MULTPLY YOUR ANSWER YOU GOT FROM ADDING 9 UNITS WITH WHAT YOU GET WITH YOUR EXPONENT.

I’m confused this is what i’m doing in class but the question is confusing