Just found out I'm cam illiterate!

[mysweetlx]

I'm contemplating stepping up to a "big boy" cam soon, and I realized I need little education in cams. I know that depending on the lift/duration of a cam it opens up and closes the valves at a specific rate, but what exactly is lift and what is duration (what does each really do)? Also, I know Ford's letter cams have the same #'s for both the intake and exhaust on lift and duration....why is this and does it help/hurt? Is it better to have higher or lower #'s, and how much difference in the 2 lift and 2 duration #'s should there be? Sorry for all the questions, I'm trying to get edumacated!