I've included the .xar file as visuals are easier than words. There are only 2 things we are playing with: the arrow and the ballroom dancers.

Ballroom dancers:
Select a graphic, text, shape, whatever down the page where you would like the arrow to appear.
Click Utilites > Names and give the object a name. I called mine 'trigger1', but it can be anything.

Arrow:
Place it where you would like it to be in relation to the top of the page.
Make it sticky.
Make it Link To Top Of Page.
Click Utilities > Web Animation > Reveal/Scroll (tab) > Reveal Animation (radio button) > Trigger Object Name (drop down box) and choose whatever you named your object.

You can use an animation to make the object appear, I used Fade, but there's a decent list to choose from.

>>> Sue Arrow.xar <<<