I did homework for two hours. =我已做了两小时的作业 I have been doing homework for two hours=我做了两小时的作业现在还在做 At high school I studied (ied=已)Spanish for one year=在高中时我已学过一年西班牙语 If you want to tell you have been doing something and still doing it. You kind of have to add one more sentence to tell people that, like现在还在做=I am still doing it now. So you would find out Chinese people always struggle in learning English grammar.

Chinese don't have verbial conjugations to indicate tenses. The language uses indicators to express. In a way, they are easier because these terms are constant. English has too many exceptions in how they are spelt. "I did homework for two hours" - 我已经做了兩小时的功课. The time indicators here are 已经 and 了. Back translating becomes I have already done two hours or work. Syntatically different but the meaning is the same. "I'll be home in five minutes" = 五分钟之內, 我回到家了. The time indicators are 之內 and 了. Back translation = Withinin five minutes, I'll be home. "At high school I studied Spanish for one year" 在高中时, 我学了一年西班牙语. 时 and 了 are the time indicators => During high school (time), I had studied Spanish for one year. "I have been doing art for over ten years" = ＋年了, 我还在做艺朮, 了 and 还在 => ten years already, I am still doing art.

1)simple past tense is usually expressed with a "了" added right after a verb. 2)simple present perfect tense can be expressed in many ways. You shall encounter them one by one in some reading materials. I don't think there is a clear grammatical rule to follow.