The rings, for making what Americans call "English" muffins, is indeed a crumpet ring. The ring is used for both things. A crumpet is made with more hydration than an English muffin. They have a holier texture than the more bready English muffin. The English muffin is made with yeast and/or sourdough.
A muffin is made in a muffin/cupcake tin. What we call a muffin is usually, but not always, sweet, and a lot like a cupcake without frosting. There is no yeast for leavening in a muffin. It is a like a small individual, sweet cake like bread.
Biscuits do not use rings. They are generally leavened with baking powder. Sometimes sourdough is used. Since biscuits are a quickly made bread, with yeast is only used in a few biscuit recipes. They are put next to each other in a pan for support. Hopefully you will end up with a light
, fluffy, individual biscuit. It is not at all like a cracker or cookie, unless you are kneading the lightness out of it. Then it is called a mistake, or what my husband called hockey pucks, when I was first learning to make them.