what is the relation netween genes,dna and chromosomes ?

Chromosomes are made from DNA. Genes are short sections of DNA. 

DNA (deoxyribose nucleic acid) molecules are large and complex. They carry the genetic code that determines the characteristics of a living thing. A gene is a short section of DNA. Each gene codes for a specific protein by specifying the order in which amino acids must be joined together. The cell’s nucleus contains chromosomes made from long DNA molecules.

You can refer to the figure given on the below site for better understanding of this relationship:

http://publications.nigms.nih.gov/thenewgenetics/chapter1.html