Questions

This information, contained in the Head part of a web page, is editable in NUZ > Publish > Sites (in the old User Zone it was Publish > SiteStyle).
Title is what appears at the top of the browser window - it is an important piece of information.
Description and Keywords are not visible to visitors but are used by search engines - they are called Meta tags.

The pages Title and other Head information can (and should) change for each page - indicating the page's content, current date etc.
On Netcells (and on your site if you so choose) each image's Keywords (tags) also show in the page's Keywords.
Be as specific as possible in your Description and Keywords - this will improve your site's search engine rating.