Well, first you need to have the audio file on your computer. Then you can simply drag-and-drop the file into any Anki field. Finding the file is the time-consuming part. I got some of them from Naver, some of them from textbook CD's, some from TTMIK. But it's a slow process.
The other option is to use a plugin that generates the audio automatically. I have no experience with such plugins so I can't help you there, sorry.