Why is chirality important in biochemistry?
Why? If someone stretches out their right hand to shake hands with you, can you shake their hand with your left hand?
The answer is NO, of course you cannot, even if you're a contortionist. Why not? Because of the chirality of your hand, or the handedness of left and right hands. Try it: right hands can clasp each other easily, as can left hands. Likewise, we can't slip a left glove over a right glove without turning one glove inside out (and inverting its chirality).
What we can appreciate on a macro scale with hands and gloves also operates on a molecular scale with sugars and proteins. Biological chemistry features a great deal of handedness: simple sugar is right-handed; left handed glucose is not metabolized. Why not? Because the biological enzymes that act on the glucose are themselves handed, and are not configured spatially to act on left-handed glucose, even if this isomer is chemically identical to its mirror image.