the present perfect tence (have\has + PP ) is used 2 talk about actions that happend at an indefinite time in the past , but that have important in the present when we refer to a definit time in the past , we use the simpel past tence.
you ever studied
(any time from past to present) .
B: yes I took
a course last year .
(specific time n the past ).
already, yet , and , still are three more expressions of indefinite time used with the PP tense
A: what has
the new principal accomplished so far
B: she promised to hire ten teachers in three years , and she's already hired
A: she also promised to put new computers in the classroom . has
B: well, I'm sorry to say she hasn't done
that yet , and she still hasn't lowered
tuition. but I'm sure she will. she's the best
principal we 've ever had
* *STILL Have many kinds and when It come with the present perfect to be negative.