If something is operational, it’s up and running and ready to go. If you’ve been waiting for a new skating rink to open, you’ll jump for joy when it’s finally operational.
When something is operational, it's ready to use or is already in use. Don’t get on an elevator that’s not fully operational unless you like getting stuck. Any gadget being used is operational. If someone calls you and you pick up and talk, then both phones are operational. If the compost bin you’ve been working on is operational, go ahead and throw in the banana peels. Operational things are functional. If your skates are operational, lace up and go!