There are 12 effects on the third (was last before 3.9) editing tab. The best advice is to play with them. Click on Sepia and see what it does, then just click Undo. Click on Film Grain and take a look, then click Undo.  This video gives an example of all the effects.  Note: when Picasa 3.9 added 2 more tabs of editing features this ‘Effects’ tab became the third tab.  All the effects remain the same.