What is the difference between past simple and past perfect tenses? when to use which?

We use past simple to talk about things we did regularly in the past. and we talk about it in general. for example, i went to school by bus.  in past perfect, we did something in the past but we finished it at a certain time in the past. for example, i had done my homework when my friend came. that means that you finished doing your homework before your friend came.

Iwould like to talk about the role that computers play in our lives. these machines appeared quite a long time ago - in the middle of the last century. initially, computers were huge, enormous machines, but over time, their size has decreased and their quality has improved. people have invented for themselves indispensable helpers in their work, socializing with friends, and entertaining themselves. computers help us make our shopping lists, remind us about important appointments and anniversaries, help us answer the telephone. we can`t imagine our lives without computers. many people have got used to such state of things and they can no longer do without  computers. so now we can see a kind of dependence on computers and computer games. of course, this is bad, because it destroys people, ruins their health and lives. as the result they can end up going crazy because computer addiction is akin to drug addiction, very difficult to recover from. thus, i believe that we should be able to control their actions and not to make ourselves slaves of "iron robots" letting them ruin our future. i believe that we should not overuse the benefits provided to us by computers. otherwise modern technology will devour us.

Present perfect tense- это настоящее совершенное время . время present perfect tense обозначает действие, которое завершилось к настоящему моменту или завершено в период настоящего времени. мы используем это время, когда нам не важно когда это действите было совершено, а важен сам результат.  слова маркеры (показатели времени ) для present perfect tense: already, just, never, yet ,recently, this week, this morning. формула образования present perfect tense: have/has + v3 (от неправильного глагола , если же глагол правильный, то к глаголу без частицы to добавляется окончание- ed. например: i have already done my homework.(have +v3 , do -done) she has cleaned her room yet.(has+ v ed , clean- cleaned) .