OK, this has almost got to be a troll (tipoff being "old light bulbs", that sounds like someone posing as a newb/idiot), but, WTF??
The glass is to enclose the vacuum inside, hence the phrase "vacuum tube". Inside there are filaments just like a conventional light bulb. These usually heat a plate, which can then emit electrons via thermionic emission. This emission can be controlled by altering the voltages on the various parts. This permits many applications like amplification.
Almost anything we do today could theoretically be done using tubes instead of transistors, given the necessary input power. There are still many applications that are better done this way than with transistors, particularly, high-power and high-frequency radio transmitters, where transistors can barely be made to work