The cytoplasm of an amoeba contains the organelles and is enclosed by a cell membrane. An amoeba uses a process called phagoctyosis to obtain food. This is a process in which projections of the cell membrane of the amoeba extend and surround the food particle, totally enclosing it. The food particle is thus internalized in a sort of "bubble" called a vacuole. The food particle can then be digested in the vacuole. The amoeba reproduces via mitosis.
Some amoebae can cause disease. For example Acanthamoeba can cause amoebic keratitis and encephalitis in humans.
Amoebae, viruses and bacteria are microorganisms. The study of microorganisms is called microbiology.
Recommended reading at Acanthamoeba and current topics on microbiology research at the Microbiology Blog