WSS Sites can simply be thought of as a collection of Lists and
Libraries (Document Libraries are just a specialized kind of List).
Security can be established at the Site or the List level.

Workspaces can also simply be thought of as a collection of Lists and
Libraries. Word can create document  Workspaces. Outlook can create
Meeting Workspaces. Meeting Workspaces have a few additional built-in
Lists (nothing that couldn't also be defined in a Team Site). Document
Workspaces created from a document in a Document Library can publish
back to the source. That's about the only differences  between Sites and
Workspaces.

A List is collection of ListItems (rows) each made up of a collection of
common fields (just like cells in a spreadsheet). Each ListItem can have
zero, one, or more attachments (documents). That said, a Document
Library is the mirror image of a List. Think of it as a collection of
documents, each associated with a collection of common fields called a
ListItem.

Both Lists and Document Libraries can be viewed using a ListView which
represents a named, selection of ordered fields which can be sorted,
filtered, grouped, totaled, styled, and paginated. Most functionality
found in a List can also be found in a Document Library and vice versa.