There are so many primers out there about BDSM I'm not sure if another one is really needed. Then again with all the basic questions asked on forums and chat rooms about BDSM, it's unlikely that my words will not be read by someone and that they will take something new from them.
BDSM is an umbrella term for Bondage, Discipline, Dominance, Submission, Sadism, Masochism. Each of these words on their own is a giant term with a lot of other vocabulary under them. Basically, anything kinky will fall under one of these terms. You don't have to know all of the vocabulary to practice BDSM but if you are really curious there are BDSM dictionaries all over the web.
On top of knowing some of the words comes learning some of the expectations and experiences, you can have in the BDSM Lifestyle. Becoming a submissive in a D/s dynamic is just like any other relationship with one very important difference. The roles are set, not fluid like a regular relationship. A dominant and submissive never switch roles (unless in agreed upon circumstances) and the relationship continues strongly as this dynamic. People can be into kinky play and only engage in their roles in the bedroom or they can be in control of their chosen role throughout their lives.
Neither is greater or less valuable to BDSM. What one chooses to do within their relationship is personal and unique. Liking other people's kinks is not required, but accepting them is looked favorably on. There are many things that I would never entertain as pleasurable or enjoyable but I can appreciate someone else's desire to do them for those reasons.
Not everyone you meet that is into BDSM wants to be part of a community. You can't make someone come out into BDSM public and say they are kinky. BDSM is still in the closet for most folks and that's okay with them. Those who want to be a part of the community you bring with you a wonderful amount of experience and personal knowledge that everyone, including new people, can learn from.
Is it a Lifestyle?
BDSM is a Lifestyle for me. I live it all the time, it's who I am. This is not the case with over half of the known BDSM population. The range of participation varies greatly. I can't say that I know exact numbers, but I know that out of 10 people I could meet in a room, 7 of them probably do not identify as Lifestyle BDSM'ers. That's fine with me, we can still chat kink and not get all uncomfortable because we aren't EXACTLY alike, right?
There are many different roles you can play in BDSM as well, from Top, Dominant or Master to bottom, submisssive and slave. There are also variations on these roles as well depending on the type of dynamic you want. You could be in a Daddy/little girl or Mommy/little boy dynamic. You could be in a Poly Master/slave household where you are the alpha. You could just be kinky and love the fun stuff in the bedroom. It's all available to you.
What's the Big Deal?
BDSM is a big deal to those that have anything to do with it because it turns them on in some way; sexually, intellectually, emotionally or all of the above. BDSM is not always sex driven, but it can be. The kinky among us consider it almost a sexual orientation; even I've given this idea a thought or two on my blog.
Is it Safe?
Depends really on what you define as safe. BDSM has two different stands on safety. One is SSC; Safe, Sane and Consensual. The other is RACK; Risk Aware Consensual Kink. The only thing in common with these two is the consensuality. The interpretations are different as different can be. Justin Medlin wrote an essay titled ' SSC vs. RACK' explaining the differences between the two.