Well, the question you are asking is easy to answer but a little more challenging to execute correctly. A synopsis is just a summary of the events that occur in a story; therefore, to write one you simply have to explain what events occur in the plot.
Sounds easy, right?
The trick is to be able to tell the difference between events that are worth putting into the synopsis and ones that can be ignored. If too much is put in the synopsis won't be effective because it will take too long to read (defeating the purpose of the synopsis) but if not enough information is included the storyline will be distorted.
Here are a few steps to keep you focused:
- To be creative, it is good to start off with a "hook" that captures the readers attention by distilling the "coolness" of the book into a line or two.
- Include information about the major characters, but don't bother with the minor ones if you don't have to. Include information about what the characters want and what is trying to stop them from getting it.
- Summarize the overall conflict of the story, including the climax, and make sure to include the outcome.
If you put these things together you will have a pretty decent synopsis. Remember, it is supposed to be a short summary of a story or book...not a detailed outline or a novel in itself!