How can I clear my Mac HD storage?

How do I store my photos/docs/music and everyrhing else in my Macintosh HD into my iCloud?

I’m trying to create enough space to backup my phone into my macbook. I cant backup my phone, because I dont have sufficient space. I bought 2TB if iCloud storage to back up my phone and can’t. Also, a external hardrive and cannot seem to clear any space into either form of external storage.