Having had to write several queries and synopses over the course of the last year, I've discovered that there are differences and similarities between queries and synopses. Some information will overlap between the two, but they are two distinct, dreaded but necessary pieces that need to be constructed. How are they similar yet different, you might ask?
-Needs to be hooking, similar to a book blurb
-Do not give away the ending. It's one of the advantages you have if you write a really good query. It makes the agent and/or publisher even more interested in reading your work and possibly representing it.
-Need to mention word count, genre, etc.
-Include information about yourself. If you write under a pen name, be sure to state that. Some places might want a phone number and/or email at the bottom of your query. I would recommend putting this information so the agent and/or publisher can easily contact you.
-This is a summary. It can come across a little dry if need be, as long as it encompasses the story.
-You have to give away the ending. Sorry to disappoint, but this is what a synopsis is for. It will be difficult, but you'll have to give away that surprise you spend thirty thousand words trying to hide.
-Spend all the space you have packing in as much relevant information as possible. The query will take care of the word count, genre, etc. information.
-Once again, this is a summary, and all you are putting in the summary is information about your book, nothing about you.
Queries and synopses may seem really different, but there are some important similarities between them as well. Some of these similarities include but are not limited to:
-Use proper grammar and spelling. Agents and publishers already sift through so many emails in one day that they won't give yours a second glance if you have typos. Thoroughly scan your queries and synopses for errors, and then make sure at least one other person helps you. The more people who look at your queries and synopses, the better.
-Make them as short as possible, while including the most information possible. A good way to help with writing these is to make a list of what you want to include. For a query, that list might include genre, word count, character information, and other items. For a synopses, that list might include plot points. Don't be afraid to start out with too many plot points, but maybe indicate main points with a highlighter or a different color and do not fail to include those.
-They need to be focused. Someone who reads the synopsis should be able to understand all the major events that happened, and it might read like a summary on a Wikipedia page. A query should persuade someone who has never read your book before to pick it up, like they were at the bookstore looking for one book to take home.
-They must be edited. A first attempt almost never quite does the job right. Revise, edit, and revise some more until it's shiny and polished.
-Both are incredibly important. Want the agent or publisher to actually read the material you send? Then make sure your query hooks them and the synopsis is so interesting that even though all the main information has been revealed, the agent and/or publisher will have his or her interest sparked and will request more.
This is just a little piece of the big picture of querying, synopsis-writing, and publishing. Hope it has been useful!