This link is a bit more instructional..
http://www.ehow.com/how_2187130_calculate-net-present-value-npv.html
Basically, you want to see which option gives you the most money at the end, after taking into account the effect of inflation,cost of financing etc on each year of the related cash flow.
Guys correct me if I'm wrong, but that is a discounted cash flow. A non-discounted cash flow should just be a sum of the income/expense of all the years for that option.
I did this last year so I should be able to help more, but I tend to discard bits of memory which don't seem useful at the time