move music from my computer to iphone

I have an iphone 4s. I have a pc. I had an adroid and easily copied the music from it to my computer. now I want to put that music on my iphone. I cannot figure this out. I downloaded the itunes to my computer but the screen does not have the columns on the left that I see everyone else has (when I look on youtube for directions) I am very frustrated. I don't know the operating system, just whatever came with it when I got 3 or 4 months ago.