Each topic can have one or more files of any type attached to it by using the Attach screen to upload (or download) files from your local PC. Attachments are stored under revision control: uploads are automatically backed up; all previous versions of a modified file can be retrieved.
Normally, if you make subsequent edits within a one hour period (configuration item ReplaceIfEditedAgainWithin), Foswiki will fold together your changes. This is often the "right thing to do", as it can reduce the visual clutter of diffs.
The Search function is very powerful. Searches using a RegularExpression play an important part of tapping Foswiki's full potential. Unfortunately RegularExpressions can be incredibly obscure to the uninitiated.
WYSIWYG is an acronym for for "What You See Is What You Get". Foswiki allows you to edit content using a WYSIWYG editor. This editor lets you edit the topic as it will appear when you save the topic, just like a text processor.