"What makes nature work?
Chemical processes which follow well understood physical laws.
"What drives natural selection?
Any given environment makes demands on organisms living there. If some of those organisms have a structure/function that increases the likelihood of an early death or few offspring, that organism's genes will eventually die out, or at best be reduced to an insignificant level. Obversely, if an organism has some structure/function that allows it to flourish in the current environment, its genes will come to dominate the population. Simple math.