The half power point essentially establishes that a -3dB difference is half the power of any frequency played through a speaker. A mono signal played through 1 speaker is going to be 100% volume, but when played through 2 speakers you have double the speakers so essentially only need half the power from both to perceive no change in level.
There is a function on the majority of mixers called Pan. Pan/Panning is controlled by the ‘pan pots’ which have an L on the left and the R on the right, with center being in the middle. This allows you to decide which side of a stereo track you want a signal to go too. Some mixers only record a stereo track and most cameras have 2 inputs that can be assigned as Left or Right.