Ensure that the power and standby switches on the amplifier head are turned off and that the master volume knob is turned down to zero. Place the head on top of the loudspeaker cabinet. Use the speaker cable to connect the socket on the back of the cabinet to either of the two 'loudspeaker' sockets on the back of the head. Be aware that two output sockets are provided on Marshall heads because some musicians will be using a 'full-stack' set-up of two speaker cabinets.
Connect the amplifier head to the main electricity supply with the power cord. Use the jack-to-jack instrument cable to connect your electric guitar to the 'input' socket on the front of the amplifier head. Turn on the standby switch on the front of the amplifier head before turning on the main power switch.
Gradually turn up the master volume knob until you have reached the required level. You may now also use the equalization ('EQ') controls to ensure that the half-stack produces the sound you desire. The range of EQ control available to you will depend upon the model of Marshall amplifier head you own.