When do we use do,does,did

Question

its and modal auxielliries when do we use them in a ssentence

Answer 1

Do:  simple present tense for first person, second person, or third person plural:  I do, we do, you do, they do

Does:  simple present tense for third person singular:  he does, she does, it does

Did:  simple past:  I did, you did, they did, he/she/it did

Done:  past participle, requires an auxiliary: is done, am done, are done, was done, were done, be done, being done, been done, has done, have done, had done

Answer 2

Do (and its other forms) are often used in questions:

"Do you like chocolate?"

It may also be used for emphasis:

"I do want to come tomorrow, but I'm really busy just now."

Or in the negative:

"I don't (do not) want to go."

Does is just the third person version (He, she, it DOES look strange.)

Did is the past tense version for any person:

I did want to go, but now I'm not sure (emphasis on did - in the past).

He didn't tell you because you weren't there.

Did you see that?

For modal auxiliary information and examples see:

http://en.wikipedia.org/wiki/English_mod...