Twenty Fourteen not uploading images

Hi there,

I’m trying to create my website so I’m using the Twenty Fourteen theme on my Mac localhost. I’m also using XAMPP to run the WP.

I have activated the theme and parentally it is working fine. But when I try to up load the background image, there is an ERROR saying:

“Unable to create directory wp-content/uploads/2015/06. Is its parent directory writable by the server”

What does it mean?
I don’t know what to do

Thanks