Contact e-mail is the address were mail will be coming with postal forms of the site.
Language version of the site is a comma-separated list of language version of your site and the title page language should be first on the list.
Maximum depth of the menu determines the depth of the site pages hierarchy. It is not recommended to do it more than 3.
SEO - in the head of all the pages you can add 2-3 custom metatags, which seems to affect the display of your pages in search engines. Useless thing IMHO...
Note: the size of this field is 250 characters!
Style of CMS - there is a small set of different color options for CMS.
To see the changes after clicking Submit there is need to reload this page or to go to another page of CMS.