A strand of DNA consists of molecules of the sugar ribose connected to one another via a molecule of phosphate. Each molecule of ribose is also connected to one of the four bases that encode the information in the DNA. The bases are Adenine (A), Guanine (G), Cytosine (C) and Thymine (T).
DNA strands tend to form pairs, in which the different bases align opposite each other according to their ability to form hydrogen bonds. The pairing is A to T and G to C. The two strands form a helical structure.
It will be clearer if you look at this picture