How to use imac to download music on iphone?

Please tell me in detail

This is the way I do it:

Open safari

Search up on the internet youtube to mp3 converter
Open another tab and search for youtube
Search for your song
Copy the URL once you are watching your chosen song
Paste the URL into the converter box in your other tab
Click convert and your download should begin

I can't quite remember but open iTunes
And then the downloaded song will either automatically go into your iTunes songs or you will have to manually drag and drop the download once completed into your iTunes application.

I really hope this helped! I haven't done this in a while and it took me a while to be able to do it.