Add together two Date/Time Fields to get year OR months OR both

I have four columns.

Date1 | Date2 | = Years | = Months

I want to use the Date/Time Field feature in LiveCycle for the first two columns to give me a user defined start and end date respectively.

I want to sum Date1 and Date2 in columns 3 and 4 to give me either years OR months OR both.

If less than a year, then return 0 years and calculate the number of months. If more than, then calculate years AND months respectively.

I am VERY new to this. I've seen similar requests, but because I'm such a noob, I'm not quite understanding how to do this. Could I please get some help or direct me where I can learn how to do this?

Thank you in advance!