From an SEO standpoint, it is not recommended to add a “| Site Name” default text to all pages. We took the advice of SEO experts and did not allow for this.
But, you could still add it manually to the end of all of your pages if you really require this.
For the description areas:
From Settings > Default Titles & Meta > Categories, you can enter in any text you desire in the Description field and it will display on the Category Archives page. Tag archive pages are set at Settings > Default Titles & Meta > Tags
You can use the following fields also to pull in data:
Categories
%site_title% – set at Dashboard > Settings > General > Site Title
%site_desc% – Set at Dashboard > Settings > General > Tagline
%cat_name% – Category name
Tags
%site_title% – set at Dashboard > Settings > General > Site Title
%site_desc% – Set at Dashboard > Settings > General > Tagline
%tag_name% – Tag name
Unfortunately, we do not yet have a method for setting a custom description for each category. We may add this in a future release to allow you to pull in the category description, tag description, etc.