Siri maybe an overlooked piece of technology on the iPad. She is quirky, and doesn't always understand you, but the more you use her, the better it gets.
In my life, I've used Siri to help my seven year old to have limits with his iPad. This has also helped him manage his time, and to remind him to do his chores, and get organized for the next day.
I use Siri to check the weather, schedule appointments, and do some dictation when I cannot be bothered tapping it out.
But you may wish to know all of her voice controls. Why not just ask her? Open Siri (hold the home button for a second) and say, "Siri, what can you do?" And she will tell you.