Can someone explain a Jtagged Xbox in simple terms?

I wanted to have my xbox jtagged but when I look on the internet all I see is stuff like: flashing, homebrew, zephyr, falcon, jasper, xenon, opus, valhalla, and has to be older than june of 09. I don't really understand all this stuff. Also, when you have a jtagged XBOX do you flip a switch for it to work or what do you do?