The structure on DNA discovered by Watson and Crick is a result of the bonding of the the nucleic acid basepairs. There is a beautiful geometry to this pairing. The weak bonds between the bases are called hydrogen bonds.
The basepairs are strung together by the sugar/phosphate backbone.
The structure fits together to form a helix with a special geometry.
Their are two types of nucleotides. Each pairs with one of the other type: A with T and G with C.