I am really good at sciece, really bad behavior, but really smart, ecspecially when it comes to atoms and the periodic table, but how do you work out the formula?

Which formula?

h20, k, and o

Each element on the periodic table has a 1 or 2 character abbreviation, so for example H = hydrogen, O = oxygen, K = potassium, and He = helium. In describing the chemical make-up of a molecule chemists list the various constituent elements and also the number of atoms of each in a molecule. One exception - if there is only one atom of a certain element then the element is shown without a number. Thus an H2O molecule has two hydrogen atoms and 1 oxygen atom in it. C2H6 has two carbon atoms and 6 hydrogen atoms. NaCl has one sodium atom ("Na") and one chlorine atom. Molecules of pure elements may have more than one atom per molecule - for example molecular oxygen has two oxygen atoms per molecule (O2), whereas helium has just one (He).

Hope this helps - does it get at what you were looking for?