Present perfect

PRESENT PERFECT TENSE
HAVE/HAS + PAST PARTICIPLE
Used when the time is not finished or unknown
I have received only a few e-mails today.
I have visited more than ten countries.

FINISHED TIME
UNFINISHED TIME / UNKNOWN TIME
YESTERDAY
John studied Maths and English yesterday.
LAST WEEK
I visited my mother twice last week.
LAST MONTH
LAST YEAR
1991
TODAY
He has studied only English today. (but today isn’t finished, so he may study Maths before it’s over)
THIS WEEK
I have visited my mother only once this week.
THIS MONTH
UNKNOWN TIME
I have watched all Harry Potter movies.
SIMPLE PAST X PRESENT PERFECT

I have had two cups of coffee today.
I have spoken to Mark this week.
I have read all four of the Twilight books.

Negative form
I saw my grandmother last week. I haven’t seen her this week.
Sarah talked to her brother yesterday. She hasn’t talked to him today.
I paid all my bills last month. I haven’t paid my bills this month yet.