Final answer:
Introducing air, denaturing proteins, and forming a foam are the three key actions taking place when air is whipped into egg whites, leading to meringue upon baking.
Step-by-step explanation:
When air is whipped into egg whites, three things occur. Firstly, the physical action of whipping introduces air into the egg whites. Secondly, this action causes the protein strands in the albumin to unfold or denature, creating a network that can trap air. Thirdly, a foam forms as the protein network stabilizes the air bubbles, leading to the creation of a solid structure upon heating as the denatured proteins coalesce, ultimately resulting in a meringue when baked at the right temperature.