You got to have some reader app on your Android device to read the books. I use Mantano, but there are many other apps, even free ones. You use calibre to maintain your library of books on your computer, and send part of it to your device, where you read the books using a reader app.
It is easiest to only have one computer with calibre. Otherwise there will be problems with differences between libraries.
You can transfer the books from calibre to your device using many different methods: Content Server; direct file copy over the network; USB-cable; cloud service; removable sd card or Calibre Companion. So Calibre Companion is mainly an app that helps you to get the books to your device. It also allows you to open specific books with some reading app on your device.
So calibre work great with android. But you still run calibre on your PC, not on the android device.
Last edited by Adoby; 10-05-2012 at 07:46 AM.