My Theme: Tips and Inspirational Quotes for Writers
A synopsis is the summary of your book's storyline, written in a clear, factual, yet gripping way. In a synopsis you tell the literary agent or publisher exactly what happens from beginning to end - especially how it ends because a synopsis is not a teaser like the blurb; publishers and agencies want to see that your storyline works.
You only need the main plotlines and you don't have to cram the name of every single character. It must be as long or short as the agent or publisher wants it to be so check their submission guidelines. Generally a page of typed A4 is good. You may need a long version and a short version on hand.
Lots of writers hate this part of the wrting process and here is a site I've found particularly helpful when it comes to advice for writers: http://www.writersworkshop.co.uk/Synopsis.html