Now that we've taken apart the nucleotide into its two major constituents, the base and the backbone, let's first describe the DNA backbone, the part that frames it all together. These sides can also be called the twin DNA 'backbones' or ribbons, ropes or strands or many other descriptive terms, and are the two ribbons you see in DNA pictures that form those long, long strands that spiral around each other, with the rungs (bases) between them.
And that is their purpose: to hold those bases in a sequence, in a pattern, to provide a frame along which the bases can be attached and ordered. The DNA backbone needs to be made of material that both holds together well and is also stretchable, twistable, and this is accomplished through a substance made up of sugars (in DNA they are called 2-deoxyribose sugars) bonded by phosphate groups.
Think of when you boil sugar; it turns to a very taffy-like substance for awhile, which holds together well but is also very twistable and pliable, and sticks to things well once attached. Those are the properties needed for the long DNA backbone so it can have millions of bases attached to it and can be twisted into endless spirals and loops.
This website is meant to be a primer understood by the layperson, so I won't get into too fine of technical detail in describing substances; but one further important detail about DNA backbones is that the two backbones have opposite DIRECTIONS. There is a 'flow' to each, a direction in which material points to and joins into other material; differences of material are simply the different mixtures of the backbone materials, sugars and phosphates. On one strand of backbone these materials point in one direction, and on the other backbone they point in the opposite direction, a condition known as 'antiparallel'. Kind of like a mouse climbing up one leg of a ladder, while another mouse is climbing down the other leg. The opposing directions, attached to and working with each other, form the basis of all life, the Yin and Yang, up and down, woman and man. On this molecular level is where originates the beginning of all larger opposing systems working in tandem to produce a unity.
So, the 'sides' of the DNA strand are called backbones, and are made of sugar and phosphate construction, and they have antiparallel directions to each other though they run side by side. Let's move on to the rungs, called the DNA bases.