The caffeine comes in from things like coffee, tea, cola, chocolate, etc. It may also change, at least slightly, the way you think about this drug in your own life. When isolated in pure form, caffeine is a white crystalline powder that tastes very bitter. The chief source of pure caffeine is the process of decaffeinating coffee and tea. It's often used to stay awake longer - college students and drivers use it to stay awake late into the night.
Caffeine is an addictive drug.
Among its many actions, it operates using the same mechanisms that amphetamines, cocaine and heroin use to stimulate the brain. On a spectrum, caffeine's effects are more mild than amphetamines, cocaine and heroin, but it is manipulating the same channels and that is one of the things that gives caffeine its addictive qualities. If you feel like you cannot function without it and must consume it every day, then you are addicted to caffeine.