if you don't want to use an online voice recorder app like Vocaroo or Speakpipe (which are easier to use than Audacity), then
*open Audacity and hit the RECORD button (red button in upper left corner of GUI).
*then open PulseAudio Volume Control.
*hit Recording tab.
*where it says "ALSA plug-in [audacity]: ALSA Capture from"--
make sure you select "Built-in Audio Analog Stereo" and NOT "Monitor of Built-in Audio Analog Stereo".
*now start speaking into mic.