We don't think the Optoma USB-A to Micro USB 1 Meter Cable f/ PK201/PK301 needs much explaining.
First, it's designed for Optoma's miniature PK201 and PK301 Pico Projectors. Now remember that one meter equals 39.37 inches. That's how long this cable is.
So what's left? Oh, USB-A is the "regular" size USB connector that you'll find on desktop and laptop computers. The micro USB connector is the tiny trapezoidal-shaped connector you often find on cell phones—and Optoma Pico Projectors. So with this cable you can plug all sorts of devices into your Pico Projector. Now that was pretty easy, wasn't it?