Hi, Emil —
Welcome to TiddlyWiki!
Are you using TiddlyWiki Classic or TiddlyWiki5? I see you prefaced your post with [TWC], which usually means you're asking about TiddlyWiki Classic (the versions of TiddlyWiki released before 2014) and prompts me to ask whether there's any particular reason you're using the older version. New users generally like to start with the current series of TiddlyWiki, called "TiddlyWiki5" (or "[TW5]" in the Google Group here). Unless there's an old plugin or feature you really need, I'd recommend heading over to
TiddlyWiki.com and getting the latest version of TW5.
In TWC, just create a new tiddler named DefaultTiddlers. Inside that tiddler, you can list whichever tiddlers you want displayed on startup, one per line (wrapping any that have spaces in the titles [[in double brackets like so]])
In TW5, all you have to do to change the tiddlers displayed on startup is edit the field "Default tiddlers" in the GettingStarted tiddler. You can get to that same setting from the Control Panel (gear icon in the right sidebar), too.
In both cases, I'm not sure you'd want to list ALL your tiddlers in the main content area ("the river"), especially if you're creating new tiddlers regularly (as you would in note-taking). You may find that the sidebar offers better options for navigating your content as your number of tiddlers grows.