An audio mixers main role is to accept inputs from a range of musical instruments and devices and outputs a combined "sum" of all audio signals. A mixer will usually output 2 main signals; Left and Right. This allows the user to "pan" individual instruments so they are heard more prominently through the Left or Right output/speaker, known as "stereo" sound.
Computer Recording with Analog Mixers
Mixing desks are also commonly connected to PC or MAC computers and used for home and studio recordings. The simplest way to connect analog mixer to a computer is using a audio mixer to PC cable. This type of cable will allow the main Left and Right channels from the mixer to be recorded to individual tracks on your recording software. Simple, cheap and effective.
USB Audio Interface
To by-pass the "analog to digital" audio conversion performed by your computer if using the analog computer inputs, an audio interface with a USB or Firewire output is required. Depending on your computers in-built sound card, this can dramatically improve your recording quality. From small dual input devices such as the ART USB preamp, which are great for recording vocals and guitar. To larger mixing consoles with standard layouts that can be used in live applications while giving the added functionality of USB output recording. Great to recording live shows.
Firewire Audio Mixers
Mixers that feature a firewire output generally have an important feature that others do not. It enables professional DAW software (Pro Tools, Music Studio) to record each channel on the mixer, to individual tracks in the DAW. This is perfect for recording studios with multiple recording rooms. Having each instrument in a individual tracks means mixing and effects can be applied to independently, the vital key to a professional mix.