Regarding a dialogue of volume control

Issue

• We got a dialogue as the following.

  The volume control did not find any elements and/or devices to
  control. This means either that you don't have the right GStreamer
  plugins installed, or that you don't have a sound card configured.
  
  You can remove the volume control from the panel by right-clicking the
  speaker icon on the panel and selecting "Remove From Panel" from the
  menu.
  

• What does the dialogue mean?