Help with Excerpt Editor (total novice)

Hi
I’m a total novice at this. I have a blog page (Photocrati Theme) with the blogs running continuously down the page. I want to have just a heading with a few lines and was advised to instal Except Editor plugin, which I’ve done. However I have absolutely no idea what I’m meant to do now. I’ve played around with it but nothings happening. Is there an Excerpt Editor for dummies or would someone be kind enough to step me through the process.
Thanks.