Basically means that your sell order will try to be processed no matter what the price is at.. your order might not get filled for 10 minutes after you place it so it could swing wildy in either direction.
Best way is to place your buy orders / sell orders at price... doesn't mean your order will be filled at that price BUT atleast you have some control over it & not get stuck with a price your not comfortable with.
People use market orders if they need to get out fast no matter what or buy in trying to catch the ride up...
I'm still a newbie but believe thats correct, feel free to flame me if i'm wrong =)
