Under preferences, in the Tags (2) submenu and in the auto-tagging section, click the selection box for lyrics - you should see a list of lyric providers, many of which were added from the plugin. You can check which ones you want to use, and rearrange them in such a way that will give priority to the best providers. For instance, I always have A-Z Lyrics at the top. Also make sure that the "auto retrieve missing lyrics of the playing track" checkbox is enabled.