Have come across this in quite a few recipes, that mussels need to be cleaned and de-bearded. First time cooking shellfish so just want to be sure I know what they're talking about. Thanks.
The beard is also known as byssus threads. They are the filaments that the mussel uses to secure itself to hard surfaces. They are usually brownish and may appear somewhat like seaweed. Most mussels commercially available have been farm-raised so often the beards have already been removed during processing. If you have beards, grasp them firmly and pull towards the shell hinge until it comes out. You may need to use a dry paper towel to increase your grip as they can be slippery.
De-bearding simply means removing the seaweed-like fibers found sticking out of the shell. Usually you can just pull it off/out with your fingers. This is less of an issue with farm raised mussels. I usually rinse and quickly take a look at each one, discarding broken mussels and de-bearding the ones that need it.