Dominance and submission are words that we use to refer to people either taking or relinquishing some level of control. This is the psychological, emotional side of kink--pure domination and submission do not include any intense physical stimulation. But dominance and submission encompass a wide spectrum of activities. And though there are many archetypal dominant or submissive behaviors, nearly anything can be defined as a dominant or submissive act, if someone participating in it views it as such. The activities may be sexual--for instance, placing someone in bondage before having sex with them, or simply forbidding them to move. They may be erotic, without actual sex (one of my favorites is having my bare feet licked and sucked). Or they may be completely practical: a submissive who cleans his dominant's house while she is away at work.
Most kinky people have a blend of these traits, and everyone's formula is unique to them. For example, I'm primarily a sadist. But as I mentioned, I do also enjoy having my feet kissed. Someone who is primarily submissive and only slightly masochistic is most turned on by the feeling of relinquishing control. The light spanking I might give them serves mainly to symbolize my control over them... but they do also enjoy the endorphin buzz they get from it. Desires can shift over time, and be different with different partners, too.
These are intense words, and some people reject them because they fear that knowing and using them will somehow unleash desires in themselves that they can't handle. But words don't compel behavior; they only describe it. Education and self-acceptance are the keys to keeping your pleasures ethically sound, emotionally healthy, and physically safe.