do 這個詞（does是第三人稱單數(shù)形式）,大體上從兩方面來講.
1.作為行為動詞,跟其他動詞一樣,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.作為助動詞,也就是幫助主要動詞構成否定和疑問等.
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.要是變成否定句就成了這個樣子：
He doesn't do his homework in the evening.
這里加上了助動詞doesn't,而原來的主動詞does變成原形do了.