Action in unfinished time: we can use Present Perfect if the time period, referred to a completed action, has not finished: this year, this week, today, this morning (if it is still morning), this semester. We never use Present Perfect when the period of time has already passed: last year, 1 sec ago, yesterday … Revise “Present Perfect Usage 0: When we don’t use Present Perfect.“
In a nutshell (exceptions may apply)
We use Present Perfect when we have:
this year, this week, today, this morning (if it is still morning), this semester
More on Present Perfect: