If you cannot find the excerpt box, you can turn it on by going to the Screen Options tab at the top right hand corner of the screen, right under your screen name.
Open the Screen Options and make sure the Excerpts is checked off. If it is not checked off, click on the box to turn it on. You should only have to do this once. Note that all of the options in the Screen Options Box must be turned on in order for the system to operate properly.
Also note that the Excerpt box may pop up in the right hand column or underneath the text entry window, so look for it in both places.
