do词性
do是用于一般现在时的助动词，did则是用于一般过去时的'助动词。done是do的过去分词。do还有实义动词（有实在意义的动词）的解释：做，干，等。口语中，do 的否定式通常用缩写形式。例如，do not 略作don't，did not 略作didn't。助动词无法与be动词、动词原形一同使用。
do的用法
1. do用于一般现在时
例句:I often do my homework in the evening.
2. does用于第三人称单数的一般现在时
例句:He does his lessons every day.
3. did用于一般过去时
例句:They did homework yesterday.
4. doing常用于现在进行时或者非谓语动词(暂时不提)
例句:He is doing his homework now.
5. done 常用于完成时，被动态或者非谓语动词(暂时不提)
例句:
He has done his homework.
He had done his homework before he went out.
His homework is done.
作为助动词，常用于疑问句和否定句。
1. 一般疑问句
例句:Do you like English?
2. 选择疑问句
例句:Does he go to school by bus or by bike?
3. 特殊疑问句
例句:How do you go to school?
4. 反义疑问句
例句:You like English, don't you?
5. 否定句
例句:I don't like English.
另外，也可以用于表示强调, 此时需要重读。
例句:He does need your help. (does重读，强调确实需要帮助)
还有，也可以代替其他的动词，使句子更简练。
例句:
Who cleaned the windows?
Tom did.