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

Restart Tkabber, to get the plugin loaded.
Visit the Tkabber->Customize->Chat->Attention Line
block of settings, customize as you wish.
Consult the README file for the details about using this plugin.

