Newbie Trade Question

If you say you will trade let's say 100 credits for 0 months, that means you will give 100 credits right away.

What about for 1 months? Is that the same thing as 0 months or does that mean 100 down, 100 for next month, too. It seems like only 100, not 200 - which if this is the case seems sorta silly, and they should take out the 0, but maybe I was just missing it...

Thanks!