Need formula for comparing differences of two columns.

Column A and B both contain numeric values. I want Excel to look at both and give me the numeric difference between the two in a new column C. I realize that if B is subtracted from A I may get a positive value or a negative value depending on which number is larger or a match as both values in that particular row of both columns A and B is the same.
What is the exact formula and how do I enter it to my spreadsheet.

Thanks!