What should I do to install a computer?

That's for sure, but it doesn't matter The shopkeeper asked you to help him make money, and he basically gave you all the accessories in the shop. These accessories are cheap, but you don't choose expensive ones. If you don't know, choose the popular one. You don't know much about computers. He said he wanted a 3K mainframe, so you told him that the accessories were not good, or something else, and then you got him a 4K one, which a novice basically didn't know. You have something out of date.