Apple cider vinegar is made by crushing cider apples and squeezing out their juice. Yeast and bacteria are added to the juice to ferment it and turn the juice into alcohol. This liquid is then fermented for a second time, which turns the alcohol into vinegar.
This flavored vinegar has many healthy properties and is used as a daily tonic by many people. However, by adding apple cider vinegar to your daily recipes you can obtain its benefits without needing to go down the (sometimes unpleasant) route of mixing it with water and drinking it straight down.