With most setups you are able to bring your audio directly into your computer through a microphone or line in port. On occasion, some people have found that they need to bring in audio another way for it to be recognized by their computer and/or encoder. In these cases an audio adapter or audio capture device can be a good route to go.  

A number of clients have found that the Logitech 3.5 Jack to USB Audio Adapter works very well for them.

Logitech 3.5 Jack to USB Audio Adapter