How do I explain the process of Natural Selection?

VOSSAG V - Variation: all organisms undergo varying amounts of genetic variation due to genetic mutations or environmental factors (such as geographic separation). O - Overpopulation: all populations have the ability to overpopulate a habitat.  S - Selection: Overpopulation creates selection pressures on the population. S - Survival of the Fittest: Only the fittest individuals survive in a population these selection pressures. (n.b. the term 'fittest' here does not neccessarily mean 'most physically capable' - any advantage developed a species that makes it more suited to living in it's environment will be selected for and will survive (e.g. ghecko camouflage)) A - Adaptation: the organisms that survive are well adapted to their environment. G - Genes Passed On: Advantageous genes are passed on to subsequent generations. This guide should always be modified to be relevant to the question (i.e. be specific to the organism mentioned in the question).