I bought a new iPhone 8. I had backed up my music on my computer from my iPhone 6.

I bought a iPhone 8. I had a 6 previously. I backed up the 6 to my computer. I cannot transfer my music. My computer won’t recognize this new 8. So I tried to download all the songs from iTunes again as I was told once you buy a song you don’t have to pay again for the same song. I have hundreds of hours of music I’m not willing to buy every thing again. It’s too expensive. I thought I could look in iCloud for the music but I can’t seem to get into that either. I am frustrated and getting angry. Please help me.