With this hack, you can choose to display a select amount of text from the beginning of each post as a teaser instead of showing the entire post on the front page of your blog. Then when people want to read the rest of the post, they can click a “read more” link to see the full post. This is very handy if you have lots of long articles all on one page.

From: http://www.template4all.com/forum/topic_54