Search optimization settings

The search optimization settings can be set in the Site settings > Site content > Search optimization tab.

Site title

When this is set to Auto (recommended), it uses a combination of the Site name and the active page name.  However, if you choose the Prepend with... option, you can add some additional text to this.  

Site description

This important field helps search engines understand your site's subject matter and relevance.  An objective-sounding natural language sentance is best.  If you load it with key words, you may be penalized by search engines.

Keywords, comma-separated

This field is best left blank because it is ignored by search engines.  It is available simply because many users request it.  Adding keywords a many repetitive key words may even hurt your rank.
How do I set the per-page site title and description?
This is possible.