Describe Robert Millikan's experiment and what significant info he learned?

His experiment, which was actually carried out by his graduate student, measured the charge "e" of the electron. No one had a clue what it was until then.

Protons have the same charge, but opposite sign. It is easier to do the experiment with electrons.

If you Google Millikan oil drop experient you will find many descriptions of the experiment. Here is a good short one:

http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/ryan_mcallister/slide3.htm