Physical Characteristics -
DNA is described as a double helix.  It looks like a "twisted ladder".  It is a double stranded chemical which is located in the cell's nucleus tightly coiled around proteins called histones.  These packages of DNA & proteins are twisted & folded into a chromatin (which cannot be seen with a microscope).  DNA can only be seen during cell division (mitosis) as chromosomes so they can easily separate. 

Chemical Characteristics -
The sides of the "ladder" are made of the Sugar Phosphate backbone.  The rungs of the ladder is made of the bases Adenine-Thymine & Guanine-Cytosine.  The single unit (monomer) which comprises DNA is a nucleotide.