1、作实义动词，也叫形为动词。和普通的动词一样，有自己的实际意思，表示“做”。
例如：do 、homework, do exercises等。
当主语是I/We/You/They或者复数名词时，动词用do。
例如：I often do my homework in the evening .
当主语是He/She/It或者其他单数名词时，动词用does。
例如：
She often does homework in the evening .
2.作助动词，无实际意思。通常用于疑问句和否定句。
(1)用于一般疑问句。直接在句首加上do/does，注意大小写和部分人称及动词的变化。
例如：
I like apples.
Do you like apples?
Yes, I do. /No, I don't.
当主语是三人称单数时，用does.
例如：She likes apples.
Does she like apples?
Yes, she does. /No, she doesn't.
(2)用于否定句时，在句子中加上don't或者doesn't.
例如：I don't like apples.
She doesn't like apples.
扩展资料
do在句子中：
1、 构成一般疑问句
Do you want to pass the CET? 你想通过大学英语测试吗?
Did you study German? 你们学过德语吗?
2、 do + not 构成否定句
I do not want to be criticized. 我不想挨批评。
He doesn't like to study. 他不想学习。
In the past, many students did not know the importance of English. 过去，好多学生不知道英语的重要性。
3、构成否定祈使句
Don't go there. 不要去那里。
Don't be so absent-minded. 不要这么心不在焉。
说明： 构成否定祈使句只用do，不用did和does。
4、放在动词原形前
Do come to my birthday party. 一定来参加我的生日宴会。
I did go there. 我确实去那儿了。
I do miss you. 我确实想你。