Question

what is difference between natural selection and genetic drift

Answer 1

Natural selection provides a force to evolution. For example, if the climate turns colder, those incapable of dealing with it will die, and only those who are statistically better at dealing with colder temperatures get to reproduce, so the species moves genetically because of outside influences and therefore 'adapts' to the new climate over thousands of generations.

Genetic drift is moving the species genetically simply because of random resampling. All organisms have variation, so there will be tiny differences accumulating all the time. Let's say you generate N random numbers with uniform distribution between 0 and 100. The mean average might be 49.937. 

Answer 2

natural selection is that where the nature selects a species which is fittest and can survive whereas

genetic drift is variation in the number of different genotypes in a small population, owing to the chance of disappearing of particular genes as individuals die or do not reproduce.