The configuration page is where you will find many of the default setting for your gpEasy site.
This is the title of your web site. It is what gpEasy will use in the "title tag" for search engines. If you leave this blank only the page's title will be displayed as the title tag.
This is where you enter the keywords for your site. These are only used by search engines.
As of gpEasy 1.7+ keywords are also available on a per page basis via "rename/details" when editing a page. The keywords found here in the configurations will be appended to every page's keywords as these are the keywords for the entire site. If you do not want these site wide keywords appended to each page then you would leave this field blank which will lead to only the keywords entered in the page's details being added to the page.
This is where you enter the description of your site. This is used only by search engines. The same goes for descriptions as keywords above.
This gives you six styles to choose from. These are the styles your images will be displayed in when using ColorBox. You can read more here 
This option will turn off HTML Tidy.
Hide gpEasy Link
This option will disable the "powered by gpEasy" link found within the admin links usually within the footer of most themes.
The other options not discussed here are either obvious or for advanced users.