All operating systems have some form of volume control application. They vary greatly in appearance.

In the playback mixer you need to make sure that there is output to the speaker (usually wav or wave is the slider name). Do not turn on anything labeled boost or 20db boost.

The Mic may need to be muted in the playback mixer, or you may hear yourself.

The Record Mixer is a separate set of controls which influences sending sound to the other party in a call. Make sure the Mic is not muted and that boost options (sometimes hidden under an Advanced button) are off.