once you have them in the tank for a while I hear your should take them out and lightly squeeze them out because they can soak up waste, excess food, etc.
I have a handful of them, they are my favorite aquarium plant
^I second what the above members said. Squeeze them out over the sink and shake them out in old tank water with every water change to get them clean. Rotate them each water change too. They do need some sort of light, however I have found them to sustain themselves just fine in under 1 wpg. They sometimes pearl and float in 3 wpg. Usually the ones sold at big chain stores are not Marimo/Hokkaido balls, rather just java moss wrapped around styrofoam.
The fake moss ball in the first picture is most likely Java Moss wrapped around a styrofoam ball (probably half dead with a decent amount of algae too if it's anything like the ones I've seen at the big chain stores here). It will need atleast 1 wpg of light to grow well.
You can peel the java moss off and attach it to driftwood or large decorative rocks or something using ordinary fishing line. You could even try to make a moss wall with it. You can PM me if you have more questions about it's care or what to do with it