To send a 10 second sound clip using your microphone, first you need to directly connect to your buddy.  This is done by clicking on the "Connect to Send IM Image" icon in the IM window toolbar:

Once you and your buddy have established a Direct Connection, press the "F12" key on your keyboard to record a sound clip up to 10 seconds long.  When you are done, the sound clip will be sent to your buddy and it will play though your buddies speakers.  You can have a lot of fun with this, because it's a combination of text and voice chatting.