How do I connect my phone to my computer without difficulty?

I use the USB cable to connect my iPhone 6s to my Mac computer but as soon as I plug the cable into the charger hole, the computer instantly comes up with a message saying “the iPhone “__” cannot be used because it requires a newer version of iTunes”. Does it mean to update iTunes on the computer? I’ve tried that and it doesn’t work. Maybe i’m Doing something wrong. My iTunes is up to date on my iPhone so I’m very confused. Help would be VERY much appreciated. All I want to do is sync my music.