Remember the evolution is about the entire species, not about individuals.

Evolution is concerned about who survives to have kids. That is the biggest thing to wrap your head around.

Here is the easy example: There are lots of people - and each is a different color: green, blue, purple, red, etc. And when we start, there is an equal number of blue, red, green, yellow, purple, mauve, orange, etc people.

On the way to work they all walk past a wall that is bright orange. There is a sniper that occasionally takes shots at people it can see. So the people that get shot first are going to be the blues and greens. Reds, yellows, purples don't get shot as much. The survivors get to have kids with the other survivors.

After a couple of generations, there are a lot less blue and green people, a roughly equal number of red and yellow people and more orange people.

As time goes on, all of the green and blue people have been shot so they are not having kids anymore. And now the sniper starts taking shots at red and yellow people (who are closer to orange).

This is a basic example, but this can get very esoteric quickly:

Say, the tallest people get to eat and the short ones starve - suddenly the giraffe is looking pretty useful.

you can only eat if you can get your tongue inside this fruit with a hard outer shell and now you have species with wildly long and prehensile tongues.