What is the difference between simple past and present perfect tense?
I walked to the shop is past simple and means I walked there once, at the time I’m referring to, in a complete action which is finished. I have walked to the shop is present perfect and means that at some time in the past, maybe just once or maybe more, I have walked there. It means that walking to the shop, as opposed to driving, cycling or not going there at all, is something I have accomplished. There are many other ways these tenses can be used with different meanings; this is just an example.