how do airline miles work?

Banks give you "points" for spending money. After spending thousands those "points" may add up to something like a discount on something. But when they finally do total up to something good the bank changes the rules making "points" less valuable. Meanwhile most people buy stuff and pay interest in excess of twenty percent. Just another scam from banks.

You accumulate them for journeys made with airlines and can use them towards flights on the airline the issued the airmiles. Only a certain number of seats are allocated to airmiles though so you don't get the same extent of choice as if you were paying.