TLDR: Ten wild monkeys alone in a room with a big pile of Legos on a pillar will make a mess a lot faster than if the pile of Legos laid in a pit.

Evaporation: The molecules that the water is made of constantly bump into each other, sometimes these molecules get unlucky and get punched so hard, that they are thrown out into the air. Most don't get very far, however, since they run into the air molecules, which kindly kick them back into the water. Still, if the molecules get far enough away, the can catch a breeze and escape.

Boiling: The molecules in the water are much more violent at high temperatures. At some point, a hole with no molecules will form in the water. Since the molecules mosh so violently into this pit, they end up slamming into the sides of the pit violently enough, that it expands despite of the rest of the water pushing back. That is how bubbles form. The bubbles then rise to the surface, and push the air away with their energy and numbers.