"Are you sure?" button, help, javascript

hello, I'm working on a cms for my website and i thought about a little idea
but i don't know how to execute it because i don't know javascript

anyways, i have a delete link, for example:
clicking this link will send the user to the delete page and do whatever...
i want to make that clicking the link will jump a message asking"Are you sure?",
only if the user selected "yes" it will move on to: index.php?act=delete&id=100

any ideas?

thanks ahead... Daniel