Ответ:

  1. I have known my best friend for five years.
  2. We have just finished our homework together.
  3. Have you ever been to a music festival with your friends?
  4. She has never tried extreme sports.
  5. They have already planned a surprise party for their friend.
  6. He has helped me with my projects many times.
  7. We haven’t seen each other since last summer.
  8. Has she ever written a letter to her friends?
  9. I have just chatted with my friends online.
  10. They have been friends since primary school.

В Present Perfect используется форма have/has + причастие прошедшего времени. Слова just, never, already обычно стоят между have/has и смысловым глаголом.