What happens if you scatter matchsticks (or line segments) randomly over the surface of a plane but with one rule - you cannot place a matchstick so that it crosses any existing one? The result is that the first matchsticks to fall end up structuring the patterns made by the later ones. The result is a pleasing pattern of what might be called "domains" where lines are more or less parallel. This is somewhat reminiscent of the way magnetic domains organize themselves in metals or crystals grow on a surface. You can see a similar phenomenon in biological evolution in fact where early choices structure and limit later possibilites. A good example would be the way all modern life forms make use of only 4 types of nucleotides (5 if you count RNA). We can imagine life forms that use other ones or something other than DNA and RNA but the reliance on those molecules was chosen so early in the history of life that it's now fixed.
You can change the way the app runs using the form fields too. The growth factor is a multiplier applied to the stick length each time a stick is placed. If this value is greater than 1 the sticks grow in length over time. If it's less than 1 they shrink. A growth factor of exactly 1 means the sticks stay the same length. It's a good idea to keep the values between about 0.999 and 1.001 or the sticks grow or shrink too fast. After changing the stick length, the growth factor, or any other parameter, you should press the "update" button to apply your changes. It's a good idea to pause the app while you make changes. To start a new matchstick world just click "Run". You can pause and restart the world with that button as well. The "Reset" button just clears and restarts the world from the beginning. You can also change the color of the new matchsticks by entering the hex code for the new color in the "Stick Color" field.