**Present perfect: the present perfect is often used with since and for to talk about situations that began in the past and continue up to now. The present perfect can also express an event that has occurred repeatedly from a point in the past up to the present time the event may happen again.
FORM: SUBJECT +HAVE/HAS+ PAST PARTICIPLE
*Positive sentence: I have known Tom since I was in high school.
*Negative sentence: I haven’t known Tom since I was in high school
*Question sentence: Have you ever known Tom since you were in high school?
*Question-negative sentence: Have you not known Tom since you were in high school?

NOTES
-***The adverbs are :ever, never, yet, still, already, just, recently…
***When we use since adverb we used this form: present perfect+ since+ simple past+…
*For example :My father has worked in the factory since last year.
***Already comes at the end of a sentence or comes between have or has.
*For example : I have already taken it or I have taken it already.
***Yet comes at the end of question or negative sentence.
*For example: I haven’t saw this film yet. or have you ever saw this film yet?