Organisms expend so much energy on complex structures that selection must have crafted them for some 'purpose'. It would be too big of a waste of energy otherwise. Dawkins then introduces the concepts of reverse engineering and utility function. Reverse engineering means deducing the purpose of some unknown object that at least appears to be designed. In living things this means complex structures.
Utility function refers to the thing which the engineering is attempting to preserve or enhance.
Those that succeed maximise their DNA replication. It is ludicrous and wasteful only from the point of view of a rational economic planner thinking in terms of maximizing efficiency. Dawkins' point can only be made by anthropomorphising DNA as if it is intentionally maximising its survival. There is only an 'illusion' of intentionality. With all these illusions one cannot help but at least expect that, at the very least, there is an illusionist behind it all.