I am completely new to molding and I went over to look at all the great molds. I feel silly asking this, but all of the molds seem like a positive instead of a cavity I could fill. Are they designed to press down onto the top of a material and make an impression? I did read about judging dimensions on the web site, but am not sure how to tell if a mold has more than one cavity. Any tips you could give me would be great, because I would like try these out, and an Oops Sale is perfect for me.