I have a new iMac and most of my songs are greyed out and have a dotted circle

OK, just got a new iMac and connected my iPhone 6, synced it to the new Mac.

Most of the songs (on the iMac) are now greyed out and have the dreaded dotted circle next to them!!

I've tried to read other posts from 2013 on this problem, but there's sooooo much to read, I've lost the will to live!

Additionally, I pay for my songs to be stored on the iTunes Cloud (probably a mistake?).

How do I get all the songs 'back to normal' on iTunes? All my music still appears to be on my iPhone, what do I need to do please?

Thank you.