Both simple and facilitated diffusion are spontaneous, meaning they require no energy for it to occur. Simple diffusion is for nonpolar molecules because they are able to pass through the nonpolar/hydrophobic membrane easily, whereas polar (hydrophilic) molecules have a hard time. Facilitated diffusion makes it easier for polar molecules to go through the membrane WITH the help of protein channels.
So the difference is that facilitated uses protein channels whereas simple does not.