Plone Editing Guides on the Web
Content Creation with Kupu and Other WYSIWYG Editors has lots of information about editing with the Plone visual editor. The plone.org Plone 3 User's Manual includes a quicker page about adding and editing pages. In general the plone.org Documentation section has lots of useful guides, and some better ones than the above may have emerge after this page is written.
The rest of this section has some useful particulars.