I only have a little bit of experience doing monitor mix for some small college shows, but:
Headphones probably aren't necessary, as you're usually just making small adjustments at the request of the talent. For a large show, I would imagine everything would be thoroughly pre-planned and tested.
The knobs in the center horizontal stripe of the mixing console are generally "aux sends". Each vertical column is an input channel, and each horizontal row is an aux bus. The knob adjusts how much of each channel gets sent to each aux bus. There are other things that can be tweaked, like toggling whether the aux sends are pre-eq or post-eq, as well as pre-main-fader or post-main-fader. Those little banks of 2 x 4 buttons at the bottom of the sends knobs bank usually control those settings. Each band member will get their own monitor send with the appropriate mix of instruments for each. It's also possible for other types of things to be mixed in, for example a click track, or a producer or director's microphone to give instructions or information to the performers.
I would expect that most of the settings would stay static over the course of a show. The engineer might do some muting/unmuting during instrument changes, or if some performers are using in-ear monitors, and there may be some scripted adjustments if some songs are wildly different in terms of instrumentation or volume. It's also good just to have someone available to correct things quickly if there's a problem. The monitor mix console is generally pretty close to the stage, so they could, for example, hear if there was some feedback occurring and quickly drop or mute a channel to kill it.
Headphones probably aren't necessary, as you're usually just making small adjustments at the request of the talent. For a large show, I would imagine everything would be thoroughly pre-planned and tested.
The knobs in the center horizontal stripe of the mixing console are generally "aux sends". Each vertical column is an input channel, and each horizontal row is an aux bus. The knob adjusts how much of each channel gets sent to each aux bus. There are other things that can be tweaked, like toggling whether the aux sends are pre-eq or post-eq, as well as pre-main-fader or post-main-fader. Those little banks of 2 x 4 buttons at the bottom of the sends knobs bank usually control those settings. Each band member will get their own monitor send with the appropriate mix of instruments for each. It's also possible for other types of things to be mixed in, for example a click track, or a producer or director's microphone to give instructions or information to the performers.
I would expect that most of the settings would stay static over the course of a show. The engineer might do some muting/unmuting during instrument changes, or if some performers are using in-ear monitors, and there may be some scripted adjustments if some songs are wildly different in terms of instrumentation or volume. It's also good just to have someone available to correct things quickly if there's a problem. The monitor mix console is generally pretty close to the stage, so they could, for example, hear if there was some feedback occurring and quickly drop or mute a channel to kill it.