This has gotten quite popular recently! Make sure you have ample space if you decide to try this one out for yourself. Adult supervision may be required.
What's Going On?
The hydrogen peroxide (H₂O₂) has oxygen in it, as seen by the O₂ in its formula. Adding the yeast to the hydrogen peroxide took out this oxygen very quickly -- it was a catalyst, meaning it sped up the reaction. This made a lot of bubbles, as you saw.