But, like most other things seen on tv or in movies, this isn't entirely true. Here is what bdsm is mostly about...
Some people naturally prefer to be in control - they are "Tops". They get off on seeing and hearing others express pleasure. Some "Tops" even say that there are momemts of empathy, when they actually feel their lover's pleasure. Other people naturally prefer to give up control - they are "bottoms". BDSM happens when a "Top" and a "bottom" get together. A mild example is when the "Top" ties the "bottom" up, after realizing that this lover would enjoy "just laying there" and have things done to her/him, but feels guilty doing so.
Of course, chains and whips are a part of the bdsm world. After all, pain causes the body to produce it's natural drug, endorphins. And chains are the ultimate symbol of submission. But no "Top" would tie up and/or hurt her/his lover unless there was complete assurance that it would be something the said lover would very much want. A "Top", by definition, is ever attentive and would not proceed if there is any indication that the "bottom" is not enjoying the experience.
Like in any community, there are people with different needs. If you don't understand or cannot relate - do not judge. Because whatever your needs are, there are people here who complete you because their need is to fulfill yours. Like in every other community, there are people of every type, and not all of them mean you well. Hopefully, if you are a "bottom", you won't fall into the hands of someone who gets off on your pain instead of your pleasure. Unless, of course, that's what you want.