How do you make something 3-dimensional square?

Answer 1

Plumb in the vertical and square in the horizontal.

You can use a square or measurements to determine square in the horizontal plane. Use plumb bob, or level to determine if it is perpendicular to the ground. Not sure what you are trying to do.

Answer 2

it is bit difficult to make a 3 d square(cube).
the characteristic of a cube is its opposite planes should be parallel and the adjacent should be perpendicular and also all the sizes should be same.for a perfect cube
1-grind the opposite sides of a metal block to the required size by a surface grinding machine.
2- mill the second two sides using a milling machine by holding the ground surface in a vise for getting these sides perpendicular to the ground surface.
3- rotate the work piece to another 90 and clock the milled side vertically 0-0 using a dial gauge and then size the third sides.
this is the technical way to produce a cube.

Answer 3

you dont make anything square - it either is square to begin with or its not

Answer 4

make a cube out of it