What forms of diffusion are passive transport?
In facilitated diffusion, molecules move down their concentration gradients. Molecules can move from either direction (inside to outside or outside to inside) of the cell, as long as the molecule is moving to an area of lower concentration. No energy is required for facilitated diffusion.
It's just that, unlike in un-facilitated or simple diffusion, when molecules can cross a barrier by themselves, facilitated diffusion happens when molecules need a particular transport molecule to move across the cell membrane.
An animation of the process can be viewed here.
This video explains the role of membrane channels in the process of facilitated diffusion.
Video from: Noel Pauller