music purchased on pc won't sync with phone

Hi, i have two questions. I like to purchase my music on itunes on my pc and then plug in my phone to sync the music. When they installed windows 10 on my laptop i had to re-download itunes but it seems like between the two things some settings are not the same as previous which is driving me insane.

1. When i download music from my pc what setting do i have to modify for the music NOT to automatically sync with my phone without being physically connected? I want to plug the phone to have the music sync to my iphone.

2. One of the song i purchased doesn't want to automatically download to my phone like the other 15 songs i just did previous to this one. I tried plugging it in and i's not working either.

Thank you