How to show a tooltip to provide info on a graph?

[findnags]

Hi,

I want to display a tooltip to provide a brief description on what the graph is for? So for eg, I have a graph as shown below and I will have some text say '?' as show in the image.  When user mouse hover on it, it should show the description on what the graph is all about.  Is it possible? If yes, how can I do that? 

Regards,

Nagaraj