In the past we've done some "BDSM for Beginners" posts, but I don't remember seeing one in a while, so I thought I'd do one for those of you who haven't been with us as long. First, for a HUGE list of terms related to BDSM, this is a great site: http://bdsmcafe.com/resource/glossary/gloss-x.html.
Now, for furniture -- if you're going to go that far -- The Stockroom is a good place to start. Besides furniture, they have tons of other stuff too, but I found their explanations of the different apparatuses to be straightforward and easy to understand: http://www.stockroom.com
Implements. If you're going to do BDSM, you'll need some type of implements. Whether you're doing impact play, sensation play or something else, don't go buying any old thing. Buy quality. How do you know the products are quality? When they come from places like: http://www.cane-iac.com or http://www.thelondontanners.com (for those kinksters in the UK or people who don't mind paying higher shipping costs for quality goods.
And clothing...sure, you can wear whatever you want. It's not like the BDSM police are going to come and take away your kinkster card if you play in sweats and a tank top. But sometimes it's fun to get dressed up, especially if you like things like role playing. Since there are TONS of places to buy clothing you can use in BDSM play, I'm not going to list any here. But I will say this. Make sure it fits, it's not cutting circulation, and that you're not allergic to it. You laugh, but there's a lot of latex out there in the kink world.
A word about bondage, which is one common place start to explore kink. Sure, you can buy a pair of fuzzy handcuffs at your local sex shop and go for it, but you're going to tie up your submissive, you should definitely check out Two Knotty Boys at http://www.beknotty.com/wiki/index.php?title=FAQ_about_Rope_By_Dan_of_the_Two_Knotty_Boys. They'll tell you what you need to know about bondage so you don't hurt anybody.
Reading. It's not a bad idea to read some books before you really get into this lifestyle. A few good ones are SM 101 by Jay Wiseman and The Loving Dominant by John and Libby Warren. Both can be found on Amazon. etc.
Lastly, join FetLife - but be careful. http://www.fetlife.com