To use the present perfect is needed this form: has/have + past participle.
We use the present perfect to refer an action that happened at an unspecified time before now, but the exact time is not important.
AFFIRMATIVE;
People have traveled to the moon.
I have been in London many times.
NEGATIVE;
People haven't traveled to the moon.
I haven't been in London many times.
INTERROGATIVE;
Have the people traveled to the moon?
Have I been in London many times?
We can't use the present perfect with specific time expressions: yesterday, one year ago, last week, etc... but we can use with unspecific expressions: ever, never, many times, before, etc.
The difference between past simple and present perfect is that to use the present perfect is needed add have/has .
We use the present perfect to refer an action that happened at an unspecified time before now, but the exact time is not important.
AFFIRMATIVE;
People have traveled to the moon.
I have been in London many times.
NEGATIVE;
People haven't traveled to the moon.
I haven't been in London many times.
INTERROGATIVE;
Have the people traveled to the moon?
Have I been in London many times?
We can't use the present perfect with specific time expressions: yesterday, one year ago, last week, etc... but we can use with unspecific expressions: ever, never, many times, before, etc.
The difference between past simple and present perfect is that to use the present perfect is needed add have/has .
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