Unless the panel is the Main Panel (first panel in the system after the service feed) all panels have a neutral bar. Otherwise you are missing pieces. If this is the Main Panel, the neutral bar is bonded to the ground by a bus-bar. If this is the case, neutrals should all be connected to the same side of these bonded bars. Electrically it makes no difference, however it is a good practice to keep electrical panels neat and organized. If this is not the Main Panel and there is no neutral bar, STOP, PUT DOWN THE TOOLS, CALL A PROFESSIONAL. This panel is missing pieces and may be dangerous.
It is possible to have a panel without a neutral. This panel would serve only 240 volt loads where no neutral is needed, however I have not seen this done in residential applications.
To install a 50 amp breaker in a circuit panel, first turn off the power to the panel. Remove the panel cover and locate an open slot for the breaker. Connect the hot wire to the breaker, the neutral wire to the neutral bar, and the ground wire to the ground bar. Secure the breaker in place and replace the panel cover. Turn the power back on and test the circuit to ensure it is working properly.
To properly install a GFCI breaker in your electrical panel, first turn off the power to the panel. Remove the panel cover and locate the breaker slot. Insert the GFCI breaker into the slot and connect the hot wire to the breaker terminal. Connect the neutral wire to the neutral bus bar and the ground wire to the ground bus bar. Secure the breaker in place and replace the panel cover. Turn the power back on and test the GFCI breaker to ensure it is working correctly.
To wire an AFCI breaker, first turn off the power to the circuit. Then, connect the hot wire to the breaker's terminal, the neutral wire to the neutral bar, and the ground wire to the ground bar. Finally, snap the breaker into place in the electrical panel.
Without more information that appears to be a 240 volt circuit. Red & black would connect to the 240 volt breaker, white connects to the neutral bar, and ground conductor from the ground rods or ground plate connects to the neutral bar. Make sure that the bonding screw is in the neutral bar and it is screwed through to bond the distribution panel enclosure to the neutral bar.
To install a 50 amp breaker in your electrical panel, you will need to first turn off the power to the panel. Then, remove the panel cover and locate an open slot for the new breaker. Connect the hot wire to the breaker, the neutral wire to the neutral bar, and the ground wire to the ground bar. Secure the breaker in place and replace the panel cover. It is recommended to consult a licensed electrician for assistance to ensure safety and compliance with local codes.
To install a 50 amp breaker in your electrical panel, first turn off the main power supply. Remove the panel cover and locate a free slot for the new breaker. Connect the hot wire to the breaker, the neutral wire to the neutral bus bar, and the ground wire to the ground bus bar. Secure the breaker in place and replace the panel cover. Turn the power back on and test the new breaker to ensure it is working properly.
To install a 30 amp breaker in a circuit panel, first turn off the power to the panel. Remove the panel cover and locate an open slot for the new breaker. Connect the hot wire to the breaker, the neutral wire to the neutral bus bar, and the ground wire to the ground bus bar. Insert the breaker into the slot and secure it in place. Turn the power back on and test the circuit to ensure it is working properly.
To install a 30 amp breaker in your electrical panel, first turn off the main power supply. Remove the panel cover and locate an open slot for the new breaker. Connect the hot wire to the breaker, the neutral wire to the neutral bus bar, and the ground wire to the ground bus bar. Secure the breaker in place and replace the panel cover. Turn the main power supply back on and test the new breaker to ensure it is working properly.
Look to see if the 30 amp panel is fed with a two wire or a three wire. If it is a two wire then you are out of luck. If the panel is fed with a three wire then the panel should have the neutral terminated in the panel. It is this neutral that you need for 120 volt connections. You didn't state how many panel slots there are in the panel. If you are able install a 15 amp breaker into the panel and connect the wires going to the load. The black wire will go to the breaker and the white wire will go to the neutral bar in the panel.
To wire a GFI (Ground Fault Circuit Interrupter) breaker, first turn off the power to the circuit. Then, connect the hot wire to the breaker's terminal, the neutral wire to the neutral bar, and the ground wire to the ground bar. Finally, attach the breaker to the panel and turn the power back on.
To install an AFCI breaker, first turn off the power to the circuit you are working on. Remove the panel cover and locate the breaker slot. Insert the AFCI breaker into the slot and connect the hot wire to the breaker terminal. Connect the neutral wire to the neutral bus bar and the ground wire to the ground bus bar. Secure the breaker in place and replace the panel cover. Turn the power back on and test the AFCI breaker to ensure it is working properly.
To install an AFCI breaker, first turn off the power to the circuit. Remove the panel cover and locate the breaker slot. Insert the AFCI breaker into the slot and connect the hot wire to the breaker terminal. Connect the neutral wire to the neutral bus bar and the ground wire to the ground bus bar. Secure the breaker in place and replace the panel cover. Turn the power back on and test the AFCI breaker to ensure it is working properly.