OK, Julia, this is only because, well, your name is Julia 😉
say $whole_story is the entire text in the database and you want to only show say the first 10 characters, then
$lngth = 10;
$summary = substr($whole_story,0,$lngth);
Now $summary is what you can display. You could also use explode() the $whole_story delimited on a period to give you (potentially) the first sentence (unless things like Dr. Mr. etc are in the first sentence, or it ends with a ? or ! but you can incorporate that as well.