Centering an ad on my site

I am new to html code, but I have learned a few things like adding <br> before and after the code to create spacing above and below the ads.
No I have a sponsor that would like to have the ad under out logo it is there but is there away to center that ad. ie.. like the <br> code.
Just wondering thanks

Code:

<center></center>

Place around the ad code.

Thanks I will try that

slg it worked thanks