The simple past tense means "an action or state that ended before the current moment, or an action that was often repeated in the past." Strictly speaking, what was said in the past has nothing to do with the present, it is only a narrative or a recollection of what happened in the past.

The actions in the present perfect tense also occur in the past, but its purpose is to emphasize the results or influence of actions that happened in the past on the present, and to say the present through the past.

syntactic structure

Positive form

Subject+verb past tense+others.

She came to help us in those days.

negative form

Subject+No? +predicate verb prototype+others.

Add did before the action verb and restore the action verb at the same time.

I didn't know you liked coffee.