How do you start a summary?
A good summary should serve two purposes: recount the major points or events of a text and use these to support the thesis, or "big idea," of the text. I recommend doing some pre-writing to try and answer the following questions. Hopefully, by answering these questions, you will have written enough content to put together a draft of a summary.
What is the thesis, or "big idea?" What do you think the author's purpose was in writing this text? Is there a particular message or lesson the author wanted to convey?
What happened? Do the events or major points of the text support the thesis? If so, how? You may like to organize this by what happened first, next, then, and finally. You don't have to include a lot of detail here, just the most important information.
What's the background? Is the author writing about a subject from which he or she is totally removed? If so, why do you think the author wrote this text? If the text is something like a memoir, how does the author's experience relate to the greater situation? Why is this situation, time, place, or idea important?
When writing a summary, I sometimes like to imagine I am speaking with someone who is entirely unfamiliar with the text. This way, I focus on only the main idea and the most important events or evidence related to the thesis.