To burn a DVD (or CD) from an .iso file:

1. Insert the blank DVD/CD into superdrive;
2. Open "Disk Utility", and click "Burn"
3. In the File selection popup, find the .iso file and select it;
4. OK, OK, and watch the progress bar to finish.

To make copies of a DVD, follow this post http://www.kenstone.net/fcp_homepage/making_dvd_copies.html

To burn a data CD, check out http://www.macinstruct.com/node/80.