The illustration about the monkeys and the typewriters is an attempt by creationists to mislead the uninformed about how evolution works. It implies that all of the many changes needed to produce complex structures would have to happen all at once through chance.
The illustration is wrong for this reason...
Small changes happen through random chance. I gave an example of such an illustration above where a single point mutation resulted in the ability to detect UV light. Now natural selection comes into play. That lucky individual will have a better than average chance of leaving offspring in the local breeding population, and those offspring will enjoy the same advantage. On average the individuals with the mutation will breed more successfully than those without it. OVER MANY GENERATIONS the percentage of the population with the UV mutation will tend towards 100%.
The creationist's illustration of the monkeys and the typewriters is stupid one. It only makes any sense if you think about natural selection occasionally updating the manuscript on every typewriter.
Evolution is gradual. One individual with a genetic advantage does not result in the elimination of the rest of the population. It just increases their chance of having more descendants.
Meanwhile other individuals in the same breeding population will also be experiencing mutations - some of which are advantageous, and which will also have been spreading in the same gene pool. Sexual reproduction makes it possible for useful combinations of genes to end up in the same individual.