I grew one and had it for years. They are very easy to grow,. I think I just stuck the stone in some compost, but it was years ago and I can't really remember. Anyway, as Katerich48 has said it was a tall skinny plant with leaves at the top - not at all inspiring. It lived for years. I think I put it out in the garden in its pot eventually and it died!
I have just found this burnhal. I obviously should have done more with my poor advocado plant.
http://www.crfg.org/tidbits/AvocadoFromSeed.ht ml