INDEX function

I am attempting to do a date conversion from regular calendar dates to a different set of dates. The user will enter the year, month, and day into the appropriate cells on the results spreadsheet and the date will be displayed.
The year part was easy using VLOOKUP but I can not figure out how to return the month and day values. I have a table with all of the dates (month: JAN, FEB, etc. as row one, day: 1-31 as column one) but I can't find a formula to work. I tried INDEX but can not seem to get it to work. I also can not figure out how to get the results to display. It needs to read YY.MM.DD using the values returned from the tables. I would be happy to send the file to anyone who might be able to help. I am a novice at this and could certainly use some tutelage!