You found a deal in the marketplace and are ready to buy. You can purchase instances in the web-based console or via an API call. If you would like to purchase using a listing ID, you can only do so with the API.
You will need in the listing id (aka offering id), which you can get by expanding a listing row in the data table.
aws ec2 purchase-reserved-instances-offering \ --reserved-instances-offering-id bec624df-a8cc-4aad-a72f-4f8abc34caf2 \ --instance-count 1
To look up the status of the purchase:
aws ec2 describe-reserved-instances