Cate,
Select an item on your slide, go to custom animation taskpane, click on add
effect button, choose between entrance, emphasis, exit, there is plenty to
choose from.
If it is slide transition effects you need, go to the slide transition task
pane and apply the effect you want by selecting it and hitting apply to all.
If you need to know more go here: http://office.microsoft.com/en-us/powerpoint/HP051924001033.aspx?pid=CH063500711033
