To use the AUX SENDS 1 and 2 for monitors: 

-Press the 'PRE' switch on each input channel that you want to use with the monitor mix, to route the AUX sends 1 and 2 'pre-fader' (so that the channel and main faders dont affect the monitor output levels).

-Use the AUX 1 and 2 knobs on each channel and the AUX SENDS 1 and 2 knobs in the MAIN section to control the levels going to AUX SEND 1 and 2 jacks to the monitors.