When we turned it on, it burst into flames and before we could extinguish it, the fire destroyed my desk.

burst 是动词，意思是"突然爆发、突然发生"。 into 是介词，表示"进入某种状态"。 flames 是名词 flame 的复数形式，意思是"火焰"。 burst into flames 是一个固定短语，意思是"突然着火、突然燃烧起来"，形容火势突然猛烈地出现。