Antibiotics are drugs prescribed to people to fight bacterial infections. They work in the body to target specific bacteria that are circulating or found withing tissues, but cannot work within cells (for example on viruses). An example is penicillin. Each bacteria respond differently to certain antibiotics and so the right one must be found for a certain infection.
They target bacteria in different ways, including, disrupting its DNA, creating an unfavourable environemtnt for it to live in and preventing reproduction.
A lot of research is still required in this area as overuse of antibiotics in populations is causing bacteria to develop resistance. The drugs then are inactive against the infection and new ones must be found. Because of this, doctors are trying to limit distribution of antibiotics.