The steps are made up of the base pairs: Adenine, Thymine, Guanine, and Cytosine.
The handrails are a phosphate deoxyribose backbone: sugars bonded by phosphate. The 2-deoxyribose sugar is a pentose, a 5-Carbon sugar. The sugars are joined by phosphate bonds form between the 3rd and 5th Carbon atoms of the sugar rings. These strands (handrails) are anti-parallel, meaning they run in opposite directions.
Hydrogen bonds attach the steps (base pairs) to the handrails. Each step can be joined to a sugar (nucleoside) or to a sugar and one or more phosphates (nucleotide).