The back seat in your 2001 Ford F-150 SuperCrew is 60-40 split-bench. The seat backs fold down to a load-floor position to accommodate cargo. Pull up on the release lever below the seat cushion, near the seat belt attachment bracket, then push the seat back forward and down against the seat cushion until it locks in place.
Fold the Seat Back Up
Pull up on the release lever, and then push the seat back up until it locks in place in its vertical position. Don't leave the seat back unlatched, even if you don't have rear-seat passengers or cargo.