Basically, sugar molecules are converted into different kinds of sugar molecules and then bound together in long strings, again with dehydration synthesis. These long strings are the glycogen or starch. Cellulose, and chitin are long-chain carbohydrates which most animals cannot easily digest. The liver stores glycogen, and can quickly convert it to sugar, dump it into the blood, and thus get energy to the body cells. If you eat simple sugar, the sugar is almost immediately available to the body, but any excess is quickly converted to glycogen or fat.
Proteins are among the most complex of the body chemicals.
The middle carbon has one hydrogen, and something else. The something else may be as simple as a hydrogen atom, or a very complex chemical ring. Amino acids are strung together into proteins by dehydration synthesis. Each protein is made up of a certain sequence of 20 amino acids. Ribosomes are essentially giant enzymes that facilitate the correct reading of the genetic code, and the dehydration synthesis to make proteins.