There are over 2000 kinds of amino acids - only 20 are used in life. The atoms that make up each amino acid are assembled in two basic shapes - left handed and right handed.
If you compare them to the human hands - each are identical to each other but different at the same time - comparing to a human hand, each has four fingers, but the thumb of the right hand is on the right and the thumb of the left hand is on the left - they're mirrors of each other.
Objects that have handedness are said to be chiral - the greek word for hand.
Handedness is an important concept as all amino acids that make up proteins in living things are all 100% left-handed - right hand amino acids are never found in proteins. If you had a protein with even one right-handed amino acid, the entire function of the protien would be lost.
This iis an issue many scientists admit they don't know - for sure - could've happened:
<blockquote><i>Many of life's chemicals come in two forms, "Left-handed" and "right-handed". Life requires polymers with all the building blocks having the same "handedness" (homochirality)--proteins have only "left-handed" amino acids..... But ordinary undirected chemistry, as is the hypothetical primordial soup, would product equal mixtures of left- and right-handed molecules, called racemates.</i>
-Sarfati, J. In Six Days, p.82
<i>This is a very puzzling fact .... All the proteins that have been investigated, obtained from animals and plants from higher organisms and from very simple organisms--bacteria, molds, even viruses--are found to have been made of L-amino [Left-handed] acids"</i>
-Pauling, L., General Chemistry Textbook, Third Edition,. p. 774</blockquote>
The Miller experiment, which I assume you've been alluding to -where Muller-Urey, in the early 1950's, created amino acids in a controlled - oxygen free - environment. What textbooks fail to mention is how that experiment would've created both right and left-handed amino acids which would be detrimental to life as the natural tendacy is for both left- and right-handed amino acids to bond together. Scientists still do now know why biological proteins use only left-handed amino acids.
<blockquote><i>The reason for this choice [only left-handed amino acids] is again a mystery, and a subject of continuous debate.</i>
-Shapiro, R., Origins of Life p. 86
<i>So we remain profoundly ignorant of how life originated. Yet the Millery-Urey experiment continues to be used as an icon of evolution, because nothing better has turned up. Instead of being told the truth, we are given the misleading impression that scientists have empirically demonstrated the first step in the origin of life.</i>
-Wells, J., Icons of Evolution p. 24</blockquote>
It's unfortunate that textbooks claim the Miller experiment as "proof" as it did NOT succeed in creating the building blocks of life (only left-handed amino acids). Here's an example from a biology textbook which dupes students into thinking that Miller succeeded:
<blockquote><i>By recreating the early atmosphere (ammonia, water, hydrogen and methane) and passing an electric spark (lightning) through the mixture, Miller and Urey proved that organic matter such as amino acids could have formed spontaneously.</I>
-Miller, K., and Levine, J., Biology, 2000</blockquote>
Notice they use the word "proved"? The only thing they proved is that life could not have begun in such conditions. Additionally, the textbook completely ignores other evidence that shows the atmosphere has always contained oxygen. Moreover, it ignores that Miller-Urey got it wrong anyways as what they produced was a mixture of left and right-handedd amino acids.
All experiements since then have failed to product even a single biological protein by purely natural processes.
