If you only use MC as an audio player or only as a video player, you may prefer a simpler looking player. Here's how to quickly do that.
You can configure JRiver Media Center to show just audio or just video by choosing Tools/Options/General/Features.
Under Services, in the tree on the left, you will find Amazon and several other stores. You can remove any that you don't want to see. Go to Tools > Plug-in Manager > Stores. Select a store and choose "Uninstall".
The default interface is called Standard View. It's the best place to organize and tag your media. For playback, you may wish to try Theater View. It's available from the View menu, or you can hit F11 a couple of times to get there.
Theater View is best used with a remote.