To generate a Table of Contents "tree" outline from individual tiddlers. start by picking a tag to use as the "root tag" of your toc tree. Any tiddlers tagged with the root tag will appear at the top level of the toc tree. To create additional levels, just create new tiddlers and tag each of them with the title of a tiddler already in the tree, and those tiddlers will appear as a level below that existing tiddler.
To display the Table of Contents, write <<toc ROOTTAG>> where ROOTTAG is the tag you chose for your starting point.
NOTE: be very careful not to tag a tiddler with the name of one of it's "children", or you will create an infinite recursion loop, where a tiddler is it's own "grandchild". If this happens, the <<toc>> macro keeps trying to render deeper and deeper into a never ending tree, and the entire document become non-responsive and you have to wait for it to timeout and then reload the whole window (without being able to save first).
You can avoid this problem simply by making sure that all the tags in your toc tree form a clean hierarchy, a top-down "tagsonomy", without any cycles.
hope this helps,
enjoy,
-e
Eric Shulman
TiddlyTools / ELS Design Studios
InsideTiddlyWiki: The Missing Manuals