do詞性
do是用于一般現在時的助動詞，did則是用于一般過去時的助動詞。done是do的過去分詞。do還有實義動詞（有實在意義的動詞）的解釋：做，干，等。口語中，do 的否定式通常用縮寫形式。例如，do not 略作don't，did not 略作didn't。助動詞無法與be動詞、動詞原形一同使用。
do的用法
1. do用于一般現在時
例句:I often do my homework in the evening.
2. does用于第三人稱單數的一般現在時
例句:He does his lessons every day.
3. did用于一般過去時
例句:They did homework yesterday.
4. doing常用于現在進行時或者非謂語動詞(暫時不提)
例句:He is doing his homework now.
5. done 常用于完成時，被動態或者非謂語動詞(暫時不提)
例句:
He has done his homework.
He had done his homework before he went out.
His homework is done.
作為助動詞，常用于疑問句和否定句。
1. 一般疑問句
例句:Do you like English?
2. 選擇疑問句
例句:Does he go to school by bus or by bike?
3. 特殊疑問句
例句:How do you go to school?
4. 反義疑問句
例句:You like English, don't you?
5. 否定句
例句:I don't like English.
另外，也可以用于表示強調, 此時需要重讀。
例句:He does need your help. (does重讀，強調確實需要幫助)
還有，也可以代替其他的動詞，使句子更簡練。
例句:
Who cleaned the windows?
Tom did.