I know that every action has a reaction, and I understand that applying a force on a surface yields a "force" from that surface to hold it up, and that it's magnitude and direction are equal and opposite, respectively. But conceptually, what is happening? Defining a force in terms of another force is not really doing it for me. What are the exact forces that are allowing this to happen? Intermolecular? Intramolecular? Or deeper?