You can add a zoom region element anywhere on your page and control its appearance using the Page and Entrance Effect sections of the Animate tab.
To add a zoom region:
From the Insert tab, select Zoom Region. Click and drag your cursor over the stage where you'd like to position your zoom region. The page will automatically zoom in on the selected region upon page load.
Tip: Try adding Show and Hide actions to zoom regions to control when the zoom is activated.