Using Excerpts

I am launching a web based newsletter using WordPress. I am posting a newsletter each week as a ‘Post’. The newsletter is a series of shortish articles. Is there a plugin that will let me turn every article (in each post) into a short excerpt…

In other words someone goes to the current (or any previous week’s newsletters (under posts) and when they see the post they are looking at a series of short excerpts

Note: I don’t want the whole newsletter to show as one single excerpt. If there is not a plugin is there coding which I can use in the html e.g I insert the coding everywhere in the one post where I want to start a new excerpt ?

Thanks