renewal group - how to use?

I'm readin this renewal group text over and over again and try to clear it out in my stressed head. What is the correct way of using this?

Let's say I have two products, one for one month recurring payments that are set to one price and another product that is for three months recurring but with slightly lower price per month. I want people who are subscribed to product one to be able to update to a three month subscription when they chose and when they do this the renewal date should be counted from the end of product one subscription.

Ok so what I'm not sure about is the value to use in renewal group field? Should it be a number (ie renewal group 1) or a text value (it says something about BASIC in the text description)

Please someone knows?

Thanks!

so

if I put 1 or basic on all products in the same renewal group, either one will work?

ok

thanks! a bit slow sometimes