Click within the applet
Start by pressing RANDOM to generate some random creatures. Set the dials below the creatures to control the characteristics of the next generations. Set the dial low on the ones you don't like and set them high on the ones with characteristics you wish to propogate. Then press GENERATE. This puts the creatures through a genetic algorithm compliant with your settings and creates the next generation.
Repeat this until you have one you like and then DOUBLE CLICK on it. This will store the creature at the bottom, underneath the machine.
If you create a creature you like but it isn't exactly what you want then DOUBLE CLICK to store it and then press RANDOM to breed the next generation. At any point, if you DOUBLE CLICK on the one you have stored, it will put it back into the breeding pool at the first position, top left, so you can reintroduce it into the GENEPOOL.
If you want a bit of a challenge, try and breed an albino creature (including white eyes) - it is possible, we have done it, but it ain't that easy!