How do we know about electrons if they are so tiny?

First of all that's a great question. How do we know about electrons if they are so tiny and small? We had to have discovered them at some point in history in order to know about them now; but when? And how? What experiments were tested to come to the conclusion that there are many little negatively charged particles buzzing around an atom?

To explain this simply, we know about electrons because of protons.

To explain not-so-simply:

Ever since J.J. Thomson's model of the atom back in 1897, probably even before that, scientists have known that atoms have to be composed of negatively and positively charged particles. In Thomson's model the particles were scattered throughout the atom's mass in a random order like berries in a berry muffin. Later on Rutherford speculated that the nucleus of an atom is positively charged (and he remains to be proven wrong) while the matter surrounding the center is negatively charged. While he was correct in both cases he was still missing the vital fact that the negative matter surrounding the center is moving. The particles surrounding the nucleus are electrons. Electrons pop in and out of the shells that they orbit inside of around the nucleus at random. One minute they are there, the next they could be across the universe for all we know. (That just shows you haw limited our knowledge of the universe is.) Anyway after Niels Bohr James Chadwick changed the atom model forever with his amazing addition; the the neutron.

So by knowing that the nucleus is positively charged and by knowing that atoms are normally neutrally charged we must conclude that a particle such as the electron must exist in order to balance out the electromagnetic charge.