How do chiral molecules differ from each other?
How does your left hand differ from your right hand? (Hopefully, you are not missing a finger!) Are they not the same?
Chiral molecules are non-superposable mirror images, that are equivalent structurally, but are not equivalent geometrically. (With your identical twin, try shaking his right hand with your left hand, or vice versa!)
Biological chemistry is rich with chirality; in its simplest form it depends on the presence of 4 different substituents at a carbon centre; the carbon is termed stereogenic or chiral.
Chiral molecules behave absolutely identically in all achiral environments (in the absence of chirality or plane polarized light).