What is the difference between a vertical sewing machine and a horizontal one?

Sandra asked:


I have just purchased a Kenmore sewing machine and I am trying to get more accessories such as buttonhole foot etc. Looking on Kenmore website some feet are to be used with vertical sewing machines other with horizontal ones and I have no idea what is the difference between the two of them. And also, if my sewing machine is Kenmore do I have to buy feet for it only from Kenmore or any other cheaper brand would work, too? Thank you in advance for your help.