Adding a popup shape (or caption) in Articulate Storyline

Hi T.A.! You can try out the following:

1. Create a new layer, then add a shape with text.

Refer to the user guide for working with layers here:

https://community.articulate.com/series/articulate-storyline-360/articles/articulate-storyline-360-user-guide-how-to-work-with-slide-layers

2. On your main layer, you can assign a trigger on button which will make the new layer appear (the layer where you placed the shape with text) when it is clicked.

Here's the user guide for working with triggers: 

https://community.articulate.com/series/articulate-storyline-360/articles/articulate-storyline-360-user-guide-how-to-work-with-triggers

Hope this helps!