Layer is usually a noun. It means, literally, a thickness of matter, usually one of several, covering a surface. For instance, in cold weather you might wear a tunic, a shirt, a jumper and a coat - altogether that would make up four layers of clothing. Or if you use blankets at night, you probably sleep under several layers in the winter (a layer can be any substance, not just material - a sandwich has 3 layers, two of bread and one of filling.)
It can also be a verb, meaning "to put or arrange in layers." For instance, there has been a recent fashion for "the layered look" where fashion magazines advise you to "layer your clothes" by wearing two or three thin shirts instead of one thick one.
A less common use of the noun is the meaning "one who lays", eg a hen that produces lots of eggs can be called "a good layer." It can also mean a shoot from a main plant, which is laid down in the soil to take root.
It can also be a verb, meaning "to put or arrange in layers." For instance, there has been a recent fashion for "the layered look" where fashion magazines advise you to "layer your clothes" by wearing two or three thin shirts instead of one thick one.
A less common use of the noun is the meaning "one who lays", eg a hen that produces lots of eggs can be called "a good layer." It can also mean a shoot from a main plant, which is laid down in the soil to take root.