The vast array of molecules that make up the human body is all combinations of a small number of dozens of basic building blocks.
Water, a molecule with two hydrogens and one oxygen atom, and "organic" molecules, which have a carbon skeleton attached to other elements, make up the majority of the molecules in the human body.
Below is a list of the elements and their relative abundances.
O2 (oxygen) - 65% of body weight
18% of body weight is made up of carbon.
10% of body weight is hydrogen.
3 percent of one's body weight is nitrogen.
1.4% of body weight is calcium.
1% of body weight in phosphorus.
A few examples of other elements include potassium, sulfur, sodium, Chlorine, Magnesium, iron, fluorine, zinc, etc.