Cyanobacteria are a type of bacteria that, despite not having chlorophyll, can perform photosynthesis. This is because they use the red light in sunlight to create energy and manufacture carbon dioxide from carbon (organic) and hydrogen (inorganic) compounds like water and nitrogen gas. When this happens, oxygen is also created as a byproduct.
Autotrophic means self-feeding or self-sustaining. Cyanobacteria are capable of synthesizing their own complex organic molecules from simple inorganic substances and grow without other sources of organic compounds such as organic detritus or other microbes that provide photoassimilates to heterotrophic organisms such as plants.