Windows Media Player vs. Itunes

Why aren't the music formats interchangeable?

My grandson set both these up for me on my computer. My first question was 'Why do I need two?'
He went on to explain that although they basically both do the same thing there are features that both have that separates them. The music formats are not interchangeable. He said I would eventually default to a favorite.

I was told that sound quality can be found in Windows Media Player. But the ease of organizing your music can be found in Itunes.

I'm too old to try and figure any of this out. It all sounds the same to me so I opted for Itunes.