Organize Itunes music files

[markwise]

I bought on iTunes store a new album, which was properly downloaded on my MBA

On other occasions I used my iMac to buy music in the Itunes store
Of course the music is then downloaded on the iMac.

Now I have several music libraries also on my iphone .
I prefer to have one central library preferably on my iMac.

I tried to select and simply drag th eplay list to my shared library .
That did not work.
How does one go about ?

Or do I -as a newby- totally miss the point of Apples concept


Please help me to organize all these music files properly.
Love to read your suggestions