do和does 在英语分别什么时候用

do是用于第一人称带词和第二人称带词，还有多人，如I,you,they。does用于第三人称单数，如it,he,she,

都用在一般现在时，does用于主语是第三人称单数的句子，如it,he,she和人名、物等。

do 这个词（does是第三人称单数形式）,大体上从两方面来讲.
1.作为行为动词,跟其他动词一样,如study,play等.他的意思是“做”等.如：
We usually do our homework in the afternoon.
He does his homework in the evening.
2.作为助动词,也就是帮助主要动词构成否定和疑问等.
We don't like bananas.
Do you like apples?
Does he like English?
He doesn't like swimming.
上面有一句He does his homework in the evening.要是变成否定句就成了这个样子：
He doesn't do his homework in the evening.
这里加上了助动词doesn't,而原来的主动词does变成原形do了.

does用在主语是第三人称单数的时候，比如he、she、it，其他的时候用do。
还有一些时候，主语是从句的时候也用does。Smoking does harm to health.