An audio mixer has many single 'mono' channels, or amplifiers, designed to condition the signal from a microphone, amplifier, instrument, or other source. Inputs can be "live" or from tape or other recording devices. The conditioning means that the channel will take a small input signal from a microphone and make it larger, and a big signal from an instrument and make it smaller, so they can be matched. the conditioning will also apply some tone controls to the signal, and can also apply some effects, like echo and technical effects like distortions. Effects are usually separate electronics from the mixer. The signal coming out of each channel of the audio mixer is then combined with all of the other channels ( mixed ) and protions of each channel are applied to the right and left output channels. This way a microphone which is a single source, can be made into a stereo one. In the mixing stage the levels of each channel are controlled so that no one channel drowns out the other, this is the art of mixing a track. Further effects can be applied to the mixed stereo output. The output of the audio mixer can be sent to a recorder, or in concert halls it can be sent to the house amplifiers for all to hear. . So the answer to your question is YES it mixes, it changes, it allows recording.