Legal music

Not so long ago, I lost all the music that I had on my computer. Downloading most of the trackers is not a big deal, but I thought about “legalizing” my favorite albums. Especially in the light of frightening posts about the withdrawal of computers from the population;) What is legalization? As the logic suggests, it is the purchase of licensed discs, or the payment of tracks in the online store. Further - more interesting. Suppose I buy CDs and rewrite them on a hard disk, or download paid music. How can I prove to severe uncles in uniform that I am not a camel? Especially in the case of online shopping?
The same situation with DVD movies. How to legally store purchased products on a computer?

I already asked this question in the comments, but I received only a couple of vague statements. I am interested in the legal side of the issue. What can you find fault with, but why not?

Thanks in advance to habra lawyers =)