Where do we find written summaries?
Here are just a few of the types of writing that involve summary:

Academic Writing

• Critique papers: Summarize material in order to critique it.
• Synthesis papers: Summarize to show relationships among sources.
• Analysis papers: Summarize theoretical perspectives before applying them.
• Research papers: Summarize to take notes and report on research.
• Literature reviews: Summarize multiple works on one topic.
• Argument papers: Summarize evidence and opposing arguments.
• Essay exams: Demonstrate understanding of course materials through summary.

Workplace Writing

• Policy briefs: Condense complex public policy.
• Business plans: Summarize costs, relevant environmental impacts, and other important
  matters.
• Memos, letters, and reports: Summarize procedures, product assessments, expenditures, and more.
• Medical charts: Record patient data in summary form.
• Legal briefs: Summarize relevant facts of cases.

Guidelines for writing summaries:

• Read the passage carefully: Determine its structure. Identify the author's purpose in writing (This will help you distinguish between more important and less important information.) Make a note in the margin when you get confused, or when you think something is important; highlight or underline points sparingly, if at all.
• Reread: This time divide the passage into sections or stages of thought. The author's use of
  paragraphing will often be a useful guide. Label, on the passage itself, each section or stage of thought. Highlight key ideas and terms. Write notes in the margin.
• Write one-sentence summaries, on a separate sheet of paper, of each stage of thought.
• Write a thesis: a one- or two- sentence summary of the entire passage: The thesis should express the central idea of the passage, as you have determined it from the preceding steps. You may find it useful to keep in mind the information contained in the lead sentence or paragraph of most newspaper stories--the what, who, why, where, when, and how of the matter. For persuasive passages, summarize in a sentence the author's conclusion. For descriptive passages, indicate the subject of the description and its key feature(s). Note: In some cases, a suitable thesis may already be in the original passage. If so, you may want to quote it directly in your summary.
• Write the first draft of your summary by (l) combining the thesis with your list of one-sentence summaries or (2) combining the thesis with one-sentence summaries plus significant details from the
  passage. In either case, eliminate repetition and less important information. Use as few words as possible to convey the main ideas.
• Check your summary against the original passage and make whatever adjustments are necessary for accuracy and completeness.
• Revise your summary, inserting transitional words or phrases where necessary to ensure coherence. Check for style. Avoid a series of short, choppy sentences. Combine sentences for a smooth, logical flow of ideas. Check for grammatical correctness, punctuation, and spelling.

How to write paraphrases:

• Make sure that you understand the source passage.
• Substitute your own works for those of the source passage; look for synonyms that carry the same meanings as the original words.
• Rearrange your own sentences so that they read smoothly. Sentence structure, even sentence order, in the paraphrase need not be based on that of the original. A good paraphrase need not be based on that of the original. A good paraphrase, like a good summary, should stand by itself.

*Taken from:
Writing and Reading Across the Curriculum. Eds: Laurence Behrens, Leonard J. Rosen. 8th edition.