Evolution is not an intentional process. It's just statistics compounding over time. Simplified example: By random chance this bird grew a 5% longer beak than its peers, which means it can catch 5% more food and raise 5% more chicks than the others. If its descendants have similar success, over time it means that their long-beak trait will become more and more prevalent in the population, and projected over thousands of years, the whole species will end up having this long-beak trait, simply because those who had it, had more kids grow to reproductive age than those who didn't.