the old man sat under the big tree and enjoyed music.the old man sat under the big tree,

the old man sat under the big tree and enjoyed music.the old man sat under the big tree,
enjoying music
为什么?这两个句子有什么不同,下面这个句子是对上面的句子做了什么处理?这里根本没有学懂,请详细讲讲,