1) Carbohydrates are organic molecules made up of carbon, hydrogen and oxygen. They act as an energy store, releasing it when needed. There are many different types. For example, the main storage carbohydrate in plants is starch. This is made up of amylose and amylopectin. Amylopectin is a frequently branched polysaccharide. This means that glucose molecules can quickly be broken from the polysaccharide (by hydrolysis) releasing energy quickly and efficiently. As a result, amylopectin is most commonly found in muscle cells as they need energy quickly. Carbohydrates also include cellulose, providing structural support in plant cell walls, and chitin, a major component in the exoskeleton of insects.
Lipids also act as an energy store. However, one of their main roles is in cell membranes. Lipids are in the phospholipid bi-layer of cell membranes and, due to their polarity, they control the movement of different substances into and out of the cell.
The main role of proteins is to act as enzymes, catalysing (speeding up and allowing) chemical reactions to take place in organisms. However, other types also have vital roles. For example, the quaternary protein in Haemoglobin in red blood cells allows it to bind to and release oxygen where it is needed in the body.
2) Enzymes are biological catalysts; they speed up the rate of a chemical reaction without being used up themselves. First, the reactant (substrate) binds to an area on the enzyme known as the active site. Here, the reaction takes place and the releases the product(s) which can then be used.
3) By speeding up chemical reactions in the body, this increases the metabolic rate. This allows us more efficient mechanisms, such as faster movement, etc.
I will try to answer the last question, I just need to double check some things. If you have any more questions, just ask.
Hope this helps