How does USB-C on the new Macbook Air Retina (also called the Macbook) connect to multiple devices?

It seems that the new USB-C connector is good for charging, good for HDMI output, good for connecting to new devices that use USB-C connectors, and good for older USB devices like an old scanner, printer, external hard drive, and video capturing box.

I suppose the older devices can be connected by using a USB-C to multi-port USB hub. However, I wonder how this USB-C connector can be connected to multiple USB-C devices, HDMI output, and older USB devices? For example, let's say an HDMI output adaptor is plugged into the Macbook, then how do you charge the Macbook, and how can another USB-C device as well as an older USB device be both plugged in?