If you use any version of windows then simply find the program called "Sound Recorder".
Win 7: START --> Type "sound recorder" in your search bar.
Win Vista: START --> ALL PROGRAMS --> ENTERTAINMENT --> SOUND RECORDER
Win XP: START --> ALL PROGRAMS --> ACCESSORIES --> ENTERTAINMENT --> SOUND RECORDER
If your computer has a built in microphone then you're all set. If not you'll need to buy one for a few dollars from any electronics shop or online.
If you don't use windows or can't use this program for some reason simply search any search engine with the phrase, "How to Record Your Voice on Computer" or something to that effect and you'll find other ways.
Once you're done head on over to the submit page and send it in along with some pics and a story.
