Microorganisms are very diverse and include all the bacteria and archaea and almost all the protozoa. They also include some fungi, algae, and certain animals, such as rotifers. Many macro animals and plants have juvenile stages which are also microorganisms. Some microbiologists also classify viruses (and viroids) as microorganisms, but others consider these as nonliving.
Some microorganisms are photosynthetic, they can make their own food from sunlight just like plants. Also like plants they give out oxygen. Other microorganisms absorb food from the material they live on or in. Some of these microorganisms can live off unusual foods such as iron and sulfur, they also absorb nutrients from food you have eaten.