If you want to make a signature for the bottom of your posts ( the little thing you see that lots of Dis'ers have with pictures and countdowns at the bottom of the posts) just go to your User CP and look on your left hand side for an option that says 'Edit Signature' and you can enter what you wish. I know there's a limit but I can't remember exactly what it is ( if anyone can clarify for me what it is that would be great)
As far as countdowns, there are a couple places you can get them:
I love my magicalkingdoms.com counter and it's awesome because you don't necessarily have to sign up for the service. Then once you get your html code you just copy and paste it into your signature which can be accessed through your User CP in the top left dark blue menu bar.