Scanning site content?

Question

Parsing

1) I need to learn how to crawl the contents of an online store so that its sections are copied to my site.
That is, I do not need to copy someone else's site entirely, but I need to copy specific sections and products in this section along with the description. And if the site will add any new product, the same new product was added to my site.
2) The same thing is needed, only that the sections turn into folders corresponding to their name on the computer. Some kind of storage.
The crux of the matter is that I don't know what technologies to learn for this. Can you advise me. Point to the right idea.