To heat a liquid until it boils; to prepare hot water, a bath, or a hot drink.
お湯を沸かしてから紅茶を入れます。
I'll boil the water and then make the tea.
朝はいつも電気ケトルでお湯を沸かす。
I always boil water with an electric kettle in the morning.
寒い日はゆっくりお風呂を沸かして温まる。
On cold days I heat the bath slowly and warm up.
To excite or rouse people; to stir up enthusiasm or excitement.
彼のスピーチは観客を大いに沸かせた。
His speech greatly stirred the audience.
そのゴールでスタジアムは一気に沸いた。
That goal sent the stadium into an uproar.