You do SEO for WordPress in the same way you would for any other site: you carry out the same tasks. There are plug-ins for WordPress to assist you in doing this. There is a SitePoint article which will give you further information, and you’ll also find discussions of the relative merits in various threads in the CMS & WordPress section of the forums.
As you seem to be a begiiner, I’d also recommend Google’s “Search Engine Optimization Starter Guide”.