Some computers have build in sound capabilities, while others require an additional component known as an expansion card or sound card. Most sound cards are used for listening to music or watching videos; other functions of the sound card are music composition and video editing. Sound cards can also be used during presentations for work or for educational purposes, even playing video games.

The sound card facilitates (directs, processes, and oversees), audio signals that are inputted and outputted both to and from the computer under the control of the computers' programs. Sound is the vibration of molecules of gas, liquid and/or solid objects that produce frequencies that are that are detectable by ears.

From 20 Hz to 20,000 Hz (20 KHz) is the frequency range that humans have the capability of hearing. Sound cards have the ability to produce these frequencies and ones above and below the human range of hearing. Sound cards can take digital data that has been recorded or generated and put it in analog format, the process is known as digital-to-analog converting. Normally external devices, such as speakers, headphones or amplifiers connect with the output port on the sound card so that the multimedia and programs can be heard.

Normally a sound card has a line in connector so that recorded audio can be transferred on to a computer, digitized and stored on the hard drive for storage, editing or processing. Microphone connectors are another common external source, for use by microphones and other input devices. Voice recognition software and voice over applications input through a microphone jack for polyphonic songs or music. Polyphony is the ability a sound card possesses, that allows more than one voice or sound to play at the same time, independent of each other.

All of today's sound cards provide actual hardware polyphony and are usually referred to as "hardware audio accelerators" but actual voice polyphony is only one of today's features. 3D sound and positional audio (Example: A quarter sounds different to the person standing next to it than it does to the person standing across the room, when the quarter falls to the floor.), and real-time DSP effects (Digital Sound Playback) are affected by the hardware acceleration of today's sound cards by being emitted cleaner and clearer.

The connection ports of the modern sound card are color coded each has a representing symbol for easy for easy identification purposes, as per the System Design Guide for PCs. The Pink connection port is for the microphone; Light Blue is for the audio input; Lime Green is for the audio output (speakers or headphones); Brown or Dark is for Right-to-left speaker; Orange is for the speaker output (subwoofer); Gold or Grey is for games ports or MIDIs (Musical Instrument Digital Interface).

The first sound card was made in 1990 and was called a Music Synthesizer Card; the card was equipped with a manual adjustment knob for volume control. The first manufacturers of sound cards were Adlab who produced OPL2, and Creative Labs, who produced the Creative Music System, which was later renamed the SoundBlaster.