in clear English - how can one use the built-in microphone in an iMac to talk on Yahoo?

Question

iMac has both an in-built Vid-Cam and a Microphone : Vid-Cam is no great problem . . . . but there are no clearly-marked controls to operate the Microphone for speech in conjuction with Yahoo IM : do such controls exist? If not specifically detailed within the iMac, has anybody worked out just how to use the in-built microphone to talk to others on the Yahoo IM? : answers appreciated!!!

Answer 1

On the Dock, open System preferences, choose Sound and then click on the "Input Tab" and select the proper source device.

If only one device, call Apple.