How are simple diffusion and facilitated diffusion similar? How are they different?

They are similar by the fact that they both don't require energie to function

Simple happend when particule travel from one side of a membrane to the other, just going trough without trouble, just following a gradient of concentration.

The facilitate diffusion use the same machanisme but occur when there are "briges" in the membrane that let the particules go through. for instance the does not like water ( it's made out of phospholipide wich is hydrophobe, just like water and oil don't mixe). therefor water goes through cell membrane using aquaporine, "holes" in the membrane that allow water molecul to pass by themeselves without any other help.

Those energy-less or passive passage contrast with other that use metabolic energy like ATP to make a molecule go through the membrane, the just like Na+/K+ pump that is used for several thing in your body, as creatng the gradient that nerve cells used to induce a message.