Too many audio producers, the fader is self-explanatory. However, we can’t assume that everyone that uses a channel strip is well versed with the exact role of the fader knob.
Many users tend to confuse the fader with the gain on a channel strip. The fader is the volume part of a channel strip that will be adjusted to achieve the required volume of a particular track and get an overall balance between the instruments in the entire project.
With channel strips that have both the fader and gain knobs, the fader knob is responsible for adjusting the volume when you need a balance. In contrast, the gain knob changes to have all the individual input signals at the same level.
A fader, just like on any mixing/audio production equipment, will control the output of a channel strip, and hence it has to be moved up to hear the sound.
A fader on a single channel will always feed the master fader. The master fader will control the sound you hear through the loudspeaker or earphones. If you take an example where the master fader is relatively low, the mix of sounds heard is controlled by the channel fader. That is to say, if you want more sound from an acoustic guitar, then push up its channel fader. Same as; if you wish to less sound of the bass guitar, then pull its channel fader down. The master fader will then do in this instance, control the level of the overall mix of sounds.