Searching for a Plugin

I’m try to find a plugin or some piece of code which allows me to show the first two or three lines of a post with a “Read More…” link when I click in a category or tag. Because i’m not fluent in english, i don’t know how to narrow my search to find what I want (and I suppose there is a plugin or something which allows me to do it)

Regards

Rodrigo de los Santos