OnMouseOver Changetext

Ok, I have no idea whatsoever how to do this, so please be thorough with any instructions.

On the left, I have a navbar, it has a list of several objects in it. What I want is when the user hovers over an object a table cell filled with text changes to fill with a description of that object. The text stays there even when the user moves the mouse off of the object but will change when the user hovers over a different object.

Sounds simple, help me out guys!

Is this JAVA or JAVASCRIPT?

I really don't care what language is used, I just need it done somehow.