You can use the “more” button (when you’re writing) to create a command that cuts off your post and the reader has to click the link to see the whole post.
Or you can make a page similar to an archives page which lists posts rather than displaying them. For this you could use the wp_get_archives function http://codex.wordpress.org/Template_Tags/wp_get_archives. You can then make that page your main page in Options > Reading.
Feel free to ask for more details, or use Google to check out the archive option. The more thing might be easiest though. Alternatively you could change <?php the_content; ?> in your index.php to <?php the_excerpt(); ?> read this for details: http://codex.wordpress.org/Template_Tags/the_excerpt.
