You can detach the keyboard of your device and use the screen as a tablet. Detaching the keyboard makes the device lighter and gives you the possibility to switch easily between laptop-mode and tablet-mode.
The device has a display with three full subpixels per pixel, resulting in a sharp and crisp picture. Pixels in some displays (like AMOLED) share one subpixel to preserve space. This can result in a less crisp, slightly blurred image.
Thunderbolt is a connection that allows you to attach external peripherals to a computer, and can carry both data and display signals. Using a single port you can connect up to six devices through a hub or daisy chain configuration.
RJ-45 ports are used for LAN (Local Area Network) connections. With more ports you can achieve increased bandwidth across a LAN, or connect to multiple networks. It also has the added benefit of not losing connection to the network if one fails.