How do lichens eat?

Lichen consists of fungus and algae. The fungus itself, unable to synthesize organic matter, feeds on the products of algae photosynthesis. The fungal hyphae supply water and mineral salts, and photosynthesis occurs in the cells of the algae, therefore the algae supplies the fungus with organic matter. Autotrophic nutrition.
Autotrophs (autotrophic organisms) are organisms that use carbon dioxide as a source of carbon (plants and some bacteria). In other words, these are organisms capable of creating organic substances from inorganic ones – carbon dioxide, water, mineral salts.