Q: I cant manually load my music with itunes on my iphone6

You cannot sync manually. You either sync music or you manually manage music. If you want to manually manage music, then you need to make sure you have the manually manage music box checked in iTunes. If you are using Apple Music, or iCloud Music, you cannot manually manage music.  Move content from iTunes on your computer to your iPhone, iPad, or iPod touch - Apple Support

Where are you looking for music at? You will find your music selection if you click on the music icon in the upper left by where you would see the iPhone icon.

It's been a few months, but I think what I did was create a smart playlist of all the checked songs, then I would drag that playlist to the iPhone icon which would then transfer the music.