To install GLX-Dock / Cairo-Dock on ubuntu 12.04
1.Open ubuntu software center.To open ubuntu software center click the Dash home from unity launcher.And type ubuntu software center in the search field.Then click ubuntu software center.
2.Type Cairo-Dock in the search box.
3.Select GLX-Dock (Cairo-Dock with OpenGL) and click install button.
4.Type your ubuntu password if needed.
5.After the successful installation click the Dash home from unity launcher.And type Cairo-Dock in the search field.Then click Cairo-Dock.