Simple For loop Question

Hi I want to just do some simple for loops to handle similar data I am always working with. For instance the first row is all titles and after that comes the day. I want to take the a specific column and put a title in row one and after that do calculations such as A1 - B2 going all the way down to the end of the data increase to AN - B(N+1). Would anyone be able to show me some basic code to start me off?

Thank you.