The study of microbes, or microorganisms, is called microbiology, which is a very popular and interesting field of science. Every microorganism has a very short life. A generation of microbes last less than 30 minutes. At the end of their generation, a microbe splits into two microbes. So they double in quantity very quickly.
Microorganisms are very very small.
They can only be seen under microscopes. The very first person who saw microorganisms is Antony van Leeuwenhoek in Holland. The animalcules he saw were actually microorganisms, which are now studied by thousands of scientists. Even though you can't see them, microorganisms live all around you. They are on your skin, on the table, on the floor you walk on, and even on the mouse you are using right now.