Their Elfa systems are extremely modular. They start by giving you a person who knows how to work their little CAD-type program. You give them dimensions of the closet, and they start designing it to best fit your needs. I went in knowing what amount of clothing I had (e.g. 30 pairs of pants, etc.), as well as what else needed to fit in the closet (bedding, wool, snowshoes, etc.). The lady at the store did an excellent job, and even helped to trim off some of the cost when I balked at the final total.
They sell you a ceiling track (well, a track that mounts at ceiling height, but on the wall), which is what everything else hangs off of, screws and drywall anchors, which you install with the ceiling track, vertical hangers, which hang on the ceiling track, and then shelves and shelf supports / closet rods/ rod hangers / whatever else you need to complete your closet.
Here is a pic of my shelves:
Oh, Glorious Day! It took me about an hour to install everything (from ceiling tracks to shelves). The shelves snap into their holders, and this can be somewhat disconcerting (I had one snap off and onto the floor once), but once you get the hang of it, it's fine and goes quickly.
Here is a picture of "after" I installed everything. This is the left side of my closet:
Here is the back wall, which faces the closet door. (I would like my mom to know that I have less than the average woman's pairs of shoes. Apparently the average American woman has 30 pairs. I have about 26. So she can't call me "Imelda Marcos" anymore! (at least, not for a while). ;-)
And here is the right side, where my clothes are. I still have not hung my pants up, because I need new hangers for them (Container Store, conveniently, sells some very handy ones that are steel and very narrow).
I still definitely need to organize, but Sweet Jesus it's awesome. I LOVE IT.
I am going back today to get a system for my coat closet. I still have a 16" deep shelf, but I think it's too short. So I am going to return that, and get a new shelf that will span over the top of my closet rod. That's all I really want. Storage up there, and then maaaaybe a shelf below? I don't know yet. The coat closet is where I am hiding my upright fan and vacuum cleaner, so I don't think I will have room for a shelf below. We shall see.