Antibiotics typically work as competitive enzyme inhibitors, they bind to enzymes and prevent them for being able to caring out certain metabolic processes. Antibiotics will effect only certain types of enzymes and typically humans may not produce these enzymes meaning it won’t have an effect on our cells but will kill bacteria. The thing is though we have “good” bacteria in our body that is also killed by antibiotics which in turn cause problems with digestion and other bodily processes. If you want an example of what an antibiotic does, it will prevent an enzyme in the bacteria from producing a membrane and it becomes easier for our bodies to attack the cell, white blood cells have an easier time killing the cell after the enzyme is inhibited. Also this is not to say that all antibiotics don’t affect human cells they may affect them slightly but typically bacteria is what’s killed