Making entries only display excerpts

In wordpress terminology those are “excerpts” (I think) so try searching for a plugin or forum messages on that subject and you might find something more useful. It’s doable if you look in wordpress codex long enough but I’ve haven’t personally tried it. But if I did,

I’d have a single.php in the theme for the full post, and modify index.php in the right place to create an excerpt and the “read more link” . You might have to do the same for date and category templates.