If you heat water to 212° Fahrenheit, then expect to see it boil — bubbling as it turns from a liquid to a vapor. It's what a watched pot never seems to do!
If the water is bubbling and roiling, then it's probably boiling. Cooks boil stuff all the time on the stove; geysers and hot springs boil naturally. And if you spill boiled red cabbage on the new white couch, mom's temper might just boil over. So you see boil can be used both literally and figuratively — to depict boiling hot liquids or boiling hot tempers.