How do you put music from itunes to iphone 5s?

I am trying to add songs to my iPhone 5s from iTunes but it is not syncing. I selected the songs I want to be synced and nothing is happening. Am I missing a step? I used to be able to add songs with no problem, is there a new way of doing it?

If someone could give me a step-by-step process that would be helpful, I am getting way too frustrated.