Most mussels sold today are farmed and come fully cleaned. Mussels only need to be washed and bearded. To beard, use fingers to pull out the clump of hair- like strands.
Before you cook mussels, clean them thoroughly. In a bowl, combine the mussels and enough cold water to cover them. Let them sit for 20 minutes.
Lift out the mussels - so you leave the grit behind - and transfer them to a colander. You may see a threadlike piece on the mussels where the shells meet. This is the beard. Yank it hard to pull it off. Discard any mussels that stay open after you pinch them closed.