It's sort of hard to describe via text but I'll try. It's a pretty basic stunt, but still make sure you always have a spotter. There's no reason to not have one

Here's for a right-handed chair... Now, I'm not a coach, just a base, so this is mostly on experience (although I've been doing it for many years) but please anyone chime in on anything you think needs chiming in on!

Also, it might be "base-heavy" since that's what I know how to do... but I'll try to describe the flyer functions as best as I can >.<
The flyer will start a few paces back (her preference). However many paces she walks, she will have to ensure she steps up with her left foot. (So left, right, left(up) is usually what I see...)
The flyer will ensure she steps up on the base's thigh, as high as she can. She will use this to push off, along with the base's shoulders and shoot straight up. She will rotate over her right shoulder to be in the 'chair' position.
On the other hand, the base will grab the flyer's ankles with their left hand while placing their right palm on the flyer's right butt cheek... for lack of better terms

The base should drive straight up supporting the flyer by her butt and pushing up with her ankle. Make sure the base locks out their arm so they are not muscling the flyer up. Flyers remember to hold their weight, keep tight while in the stunt.
Some nice-to-knows based on my experience:
- Practice the take off. Have the flyer walk her paces, place her foot on the thigh where its comfortable for the flyer to grab and shoot without rotating so the base and the flyer can get their timing; This is imperative for the stunt to work. (just like tosses.) The flyer and the base want to be "shooting up" at the same time.
- Ensure the flyer is wearing shorts or rolls up pants legs... This will help give the base a better grip on the ankle; Holding the ankle really helps with the stunt, stability, and keeps the right arm from getting tired.
- Ensure that the base keeps their right arm locked and by their head... so the chair doesnt "tilt" to the side, spilling the flyer onto the floor....
- Some people instead of holding the ankle will hold the thigh... That is preference, and I would only recommend this to base/flyers who are very different in proportion and weight (a giant dude stunting with a teeny girl....)
- For the sake of the base please remind the flyer to really give some "umph" into the push off. Use the base's shoulders and thigh to help give the momentum to shoot off.
I hope that makes some sense... Here are some videos that demostrate it pretty well.
http://www.youtube.com/watch?v=vAgawLaWE8g&feature=relatedhttp://www.youtube.com/watch?v=ldUuuoXasKo&feature=relatedHappy stunting!