this may help to you: russian perfective and imperfective, ok?
ya izuchil= yo estudié.........perfectivo/imperfecto (finished action)
ya izuchal= yo estudiaba.... imperfective/(forgot name in spanish......past action unfinished(narrative).
what lobogriego says about "yo he estudiado" is almost ok but incomplete. In fact, if you come to barcelona, ought to catalan influence, spanish speakers use always "he estudiado" with value of "estudié", but you shouldnt get worried about this. Also note, that your translation from english to spanish is not totally correct. It is better not to do direct translations from english to spanish depending on some tenses. You'll get better results just thinking the russian verbal system.