Hi @csteiger thanks for posting in the community! There are few ways to add information to a shape in Lucidchart. The first one is by adding a Note or Image to a shape. 

To add a note right click the shape and select 'Add Note' from the menu. After adding a note to a shape you will see the note icon on the top right corner of the shape. If you click on the note icon it will show the note you added.

Alternatively if you are looking for a popup message to appear when hovering your cursor over a shape you could do this through conditional formatting. For more information please see this community post which has a great example and instructions on how to do this.

Please feel free to comment in this thread or make another post if there's a different topic you'd like to discuss. Hope this helps!