you pm the buyer with (the way grnbg posted above somewhere) and put your signature with the address your shares are on in it and the other guy does same and pm this complete message preferably to you and grnbg so he can confirm that both of you are willing to buy/sell x ammount of shares for x ammount of bitcoins...hope that helps somehow
I'd like to retract my ask of 0.0261, for all 21 of my shares, and ask for the current high bid of 0.003 per share. How do we finish this deal?