One of the best places to look for an example summary is in a library record's abstract field. The following image shows the abstract (or summary) of an article available through the library:
An abstract is often written by the author of the article. It is therefore a part of an article, and cannot be used as a substitute for your own summary in an essay or as part of the annotation in an Annotated Bibliography.
If you have been asked to construct an abstract for an assignment, the following tutorial from Academic Writer may prove useful: