History panel on Lightroom 3.4

Have just started my trial with Lightroom 3.4 desktop.  Edited my first image and all was going well until I wanted to go back a couple of steps.  I know this is possible by picking your starting point in the history panel, but my problem is I don't see a history panel.  And I can't find anything among the things that I can change to bring it up.  Is there some secret to making the history panel appear?  Or is the trial version of the product not capable of showing it?  Thanks for any help.