I have a voucher for $1000 from American Airlines. How do I turn that into cash so I can use it to book a flight?
American Airline vouchers are tricky to use. The value is not cash-equivalent, it is the maximum price of a single flight you can buy with it. You cannot buy two $500 flights with it. When they gave vouchers for us as a family, we each got one, not one with an amount for everyone to fly.
The first thing to be mindful of is the expiry date. It is usually 12 months after being issued. At least all of mine were.
The second which can make it tricky is that it specifies a departure region, usually the same as where you were issued the voucher. Last time with happened I got bumped from a US connection and gave me a voucher which was only valid for US departure. To use it, I therefore had to get myself to the US first! In this case it cost more to use it than its value, so I left it expire.
One more thing, AFAIK, it can only be booked by American Airlines. Perhaps a travel agent but should ask, if you feel it is more convenient to you.