Youdothisbytakingyoursubjects, "I," "you," "he," "she," "we," and "they," andyouconjugatetheverb "tohave" asyourhelperverb, so "I have," "youhave," "he/shehas," "wehave" and "theyhave."
So, if I saysomethinglikethis: "I haveworkedhardtoday, I'm stillworkinghardnow, I wasworkinghardand I willmostlikelykeepworkinghard," sothetimeoftheactionisnotover.
"I haveworkedhardtoday." "I think I'veworkedhardtoday."
"Yeah, I'veworkedprettyhardtoday."
Thesecondsituationwhereyouwouldusethepresentperfecttenseiswhenyou'reusingthewords "for" and "since" totalkaboutsomethingthatstartedinthepast.
I couldsaysomethinglikethis: "I havelivedherefor 20 years," or "I haveworkedformybrothersince I was 20 yearsold."
So, whenyouusethewords "for" and "since," theykindofindicatetoyouthatyoushouldbeusingthepresentperfecttense.
So, thetimeatwhichyoustudiedancienthistoryisnotimportanthere.
Allthat's importantisthat I wanttoknowifyouhavestudiedancienthistory.
It's a littlebitof a trickyonetolearnasanEnglishlearner, butit's definitely a verycommonusageofthepresentperfect, totalkaboutsomethingwherethetimethatthatthinghappenedisnotimportantintheconversation.