How do you put itunes from a computer or cd on iphone x?

How do you put itunes from a computer or cd on iphone x?

Your question barely makes sense. On iphones you have an iTunes store or the music app it doesn't have iTunes as a computer does. To transfer music from a computer to an apple phone you have to install iTunes on the computer, log in with your apple ID, and use itunes on the Computer to sync with the iphone. Simply by plugging the iphone to the computer will start itunes and the sync process.
If you want a CD transferring to an iphone you have to first import it into iTunes on the computer and then sync with the iphone. Follow Goose's advice and lookup how to sync iTunes to an iphone

You don't. However, you can synch the information from iTunes on your computer to your iPhone. There are hundreds of thousands of websites telling you how to do it. Heres one of them