How does the USB power wire work?

I stripped a USB cable. The cable itself has four wires: white, black, red, and green. Each USB cable has two ends, each with a connector. One one end is a type-A connector, and on the other a micro-B connector. The type-A connector has four pins, and the type-B has five!

What are the four wires? The four colors correspond to four names. The black and red are power wires, and the white and green are data wires. Black is “GND” or ground. The red is “VBUS”, or +5 volts. The white is “D-” and the green is “D+”, where “D” stands for data.

Each pin on the connector is connected to one of the four wires. On the type-A connector:

   |                            |
   +----------------------------+
   | +========================+ |
   | |   ___            ___   | |
   +-|  [___]          [___]  |-+
     |                        |
     +------------------------+
     |  |GND|  D+  D-  |+5V|  |
     +--+===+--==--==--+===+--+
     ||||||||||||||||||||||||||
     +------------------------+

Ignoring the data pins, you can just use USB to power things. I made a USB LED light by connecting:

GND (black wire) to a 100 ohm resistor
the resistor to the short (negative) leg of the LED
the long leg to +5V (red wire)
the USB A connector to my laptop
ignore the data wires

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