Alright, first, a little bit of general introduction to polymers. A polymer is any molecule that consists of a series of smaller subunits that attach to one-another in a serial fashion. There are no further requirements on the molecule to make something a polymer, although the backbone of the molecule needs to be capable of forming strong chemical bonds, a property best exemplified in the element carbon, but it doesn't have to be carbon at all.

Protein is a polymer of amino acids. DNA is a polymer of nucleotides. Starch and cellulose are both polymers of simple sugars. Artificial polymers like nylon are composed of less natural, common in nature subunits, often containing things like chlorine and fluorine, both elements almost never found covalently bonding in nature and very hard for natural processes to get rid of (ionizing solar radiation and cosmic rays being about the only ones I am aware of). The natural polymers, of course, living things have ways of digesting those.

The basic concept is the same: you have units of molecules, each of which has two attachment points that can undergo a chemical reaction and bond to the attachment points of other molecules of the same type. What the nature of the attachment point is, as well as the properties that the resulting polymer has, vary greatly from polymer to polymer. About the one physical property that polymers do have in common is tremendous tensile strength - often greater than steel - but absolutely worthless compressional strength. This makes them great for cables or wires that hold things together.

Polymers are not all the same.Most of the major building blocks of life are polymers. Proteins are polymers of amino acids. Carbohydrates are polymers of sugars. Cellulose in plants is also a polymer of sugars, but it is very different from a sugar polymer such as corn starch. Polymers are sort of molecular strings of 'pop-beads'. Some polymers have only one type of bead, such as some carbohydrates that are polymers of the sugar glucose. Some polymers have many types of beads along the polymer chain. Proteins are made of about 20 different amino acids, which you could picture as pop beads of 20 different shapes. The different amino acids have different chemical properties, too. Some are more acidic; some are larger or smaller; some mix better with water; some mix better with oil. You can picture them as being sort of like sticky or slippery beads of various types.