There a round ball of moss that grow in the wild that way, the way they propagate is sending out runners and making new balls.
There just another type of plants for your tank but the benefit of these is they use the nitrates in the water for food, you dont have to plant them in the ground like most plants, they just sink to the bottom instead of float at the top like other plants that use the nitrates out of the water instead of the nitrates that are in your substrate to grow.