The far right hand BNC type connector is to used if the 100W amplifier is not installed. (When installed, this connector is in parallel with the amplifier input circuit.) On the right hand upper corner there are two connectors used for Two Meter transverter, transmit and receive.
The connector under the BNC connector is used for Earth (RF) ground. The lower right hand side of the rear panel houses the external control connector, D type, as well as the Parallel Port Connector, which connects to the PC parallel port. The option SDR-USB USB-to-Parallel Adapter connects to this port.
The smaller connectors across the center right side of the panel are CW/paddle connector, line output (speaker output) on sound card, high impedance output for amplified speaker or headset, line to sound card, and microphone input on sound card.