Can someone please explain these connectors to me.

Solution
The top one is a Dual Link DVI-D. This means it can only do digital video, to a screen that takes a DVI (or HDMI, with a passive adapter) port.

The lower one is DVI-I, so can be either digital or analog video. You can connect it to a DVI or HDMI screen, or use an adapter to connect it to a VGA screen.
The top one is a Dual Link DVI-D. This means it can only do digital video, to a screen that takes a DVI (or HDMI, with a passive adapter) port.

The lower one is DVI-I, so can be either digital or analog video. You can connect it to a DVI or HDMI screen, or use an adapter to connect it to a VGA screen.
 
Solution
The top connector is a DVI-D Dual link connector, the bottom one is a DVI-I dual link connector. DVI-I supports both DVI-A(analog) and DVI-D(digital), the extra 4 pins provide for the analog signal, the DVI-D connector only supports digital output, you cannot put a DVI to VGA adapter on there as it doesn't have the proper outputs.