Connect your electric instrument to the Marshall amplifier with an instrument cable. Plug the instrument cable into the designated port on your instrument and the "Input" port on your amplifier. Turn on the amplifier to hear the instrument sound through the amplifier.
Connect your amplifier to a digital mixing board if you plan on channeling output of multiple signals through the amplifier. Plug the amplifier into the "Output" channel on the mixing board with an instrument cable. Connect other instruments and microphones into assigned individual audio channels on the mixing board.
Connect the instrument or microphone to any desired effects pedals by plugging your instrument cable into the "Input" plug on the pedal. Connect a second instrument cable between the "Output" plug on the pedal and the "Input" port on the amplifier. Turn on the amplifier and pedal to hear notes produced by the instrument and modulated by the effects processor before being played by the amplifier.