My device won't show up after I connect my tablet

I have followed all the directions and I still can't get my tablet to show up on the left so that I can get the files from ADE on my PC onto my tablet. I know the tablet is connected to the PC because I can see it in Computer.

The tablet is an LG. Is that the problem? If so, can I get the files into Google Play Books instead?

I've spent all day on this and I'm ready to throw everything against the nearest wall! Help!