detail box, I am sorry,but I don't know how to say it short, please have a loo Options

[mahroofali]

how can we make a small text box appear while we point the mouse over a word or any item?
I mean,just like the help descriptions.
for example, while registering to this forum,right to the input forms, we will find a (?).while we click it, a small description pops up. How can we do that?
I am a student, and too novice,(but got sme basics in html),so try to answer accordingly. If something is wrong in my part, forgive me....