What are antigens, and how do lymphocytes “recognize” them?

What are antigens ? - Antigens is a toxin or other foreign substance that induces an immune response in the body, especially the production of antibodies.

How do lymphocyte "recognize" them ? - However, the T-cell receptor differs from the B-cell receptor in an important way: It does not recognize and bind antigen directly, but instead recognizes short peptide fragments of pathogen protein antigens, which are bound to MHC molecules on the surfaces of other cells.

Why would you choose to put this in the biology lol