Larah, as Vinicius and Chris pointed out, when you talk about events in the past, there are multiple situations that can come up: 1) something that started in the past and has ended 2) something that started in the past and is still relevant 3) something that was going on in the past when something else happened Each of these situations uses a different verb construction. As Chris mentions, the explanation of the verb tenses can get a bit involved and grammar books take many pages to explain all the options.

Hey Vinicius! Thanks for helping me.

Hey there Larah! A short explanation would be: The difference between them is that we use past simple for specific past time Present perfect for things in the past and up to now Past perfect for something that started in the past before another thing in the past for example: past simple >>> I went to school yesterday present perfect >>> I have lived in New York for 27 years past perfect>>> I had studied English before starting a new language Hope it helps you :D

Grammar books cover this in 10-15 pages. You expect someone to summarize it in 10 lines?