Numbers in a column formation mean that they are written one on top of the other such that units are in their own column, tens are in their own column, hundreds are in their own columns, and so on. when subtracting, the number being subtracted from goes above the number being subtracted.
When in column formation, work from the right and subtract the bottom number from the top number. Write the answer below in the same column. Move on to the left and repeat with the next set of digits.