A few points from what I know about them:
1. They need a fine substrate to burrow in, preferably sand. They will spend a lot of time buried under the substrate but they will travel around the tank as well.
2. They're filter feeders so the way they eat is they filter the aquarium water through their mouths.
3. They're pretty hardy but you do want to keep an eye on water parameters since they don't like ammonia and nitrates.
I've only seen them discussed as aquarium inhabitants so I don't know if they can be kept in a pond but I can't imagine why not if the conditions are right.