As usually, copy this directory under the ~/.tkabber/plugins directory
so that you get a hierarchy like this:
  ~/.tkabber/plugins
  ~/.tkabber/plugins/autoanswer/
  ~/.tkabber/plugins/autoanswer/autoanswer.tcl

Restart Tkabber, to get the plugin loaded.
Visit the "Customize->Plugins->Auto Answer" block of settings
and adjust them if needed.
Consult the README file for the details about using this plugin.

