What are these things and what's the difference? Do you need all of them to promote your book? Yeah, you probably do. So what are they?
The logline is also known as the elevator pitch. It's very short, one sentence if you can manage that. It gives the briefest of plot summary and entices the listener or reader to want to learn more. Imagine you're at a conference and an agent, or even a writer or a reader asks you what your book is about. Here's where you give your logline. It's best to have it memorized, but no one will laugh if you whip out an index card.
For SMOKE, I'd say it's a humorous Texas mystery featuring Imogene Duckworthy, an unwed mom living in a single-wide who longs to be a PI.
This gets in the genre and sub-genre, location, the main character, and her motivation.
Blurbs are fuzzy, since this word is used for two different things. One is the cover blurb, written by the author and is similar to the logline but can be a bit longer. The other meaning is blurbs written by others that you will proudly display on your cover, signed by the authors who endorsed your book. The one you write will also be used as your book description online.
The one I ended up with for SMOKE is: Imogene Duckworthy, who yearns to be a PI, has landed a job assisting Mike Mallett in Wymee Falls, Texas. Bringing home a pot-bellied pig as a birthday gift for her daughter, Nancy Drew Duckworthy, Immy discovers the body of the owner of Jerry's Jerky hanging in the smokeroom. Now she has her chance to prove her skills.
This gets into the plot a little, but doesn't give anything away. It tells the beginning of the action, how the story starts, and I hope it makes the reader want to know more.
The synopsis, however, is for an agent or editor and doesn't hold back on the plot. It should tell the whole plot, but succinctly. For a mystery, the killer is named, plus how the killer is caught or detected. In a romance, the push pulls are all spelled out, and how the obstacles to happiness are overcome in the end. For all genres, the ending is given. The synopsis tells the reader, the person you want to buy or publish your book, that you can put a plot together. I generally write a one-page, single-spaced synopsis for query letters. I capitalize each name the first time it appears and only use a few proper names, no more than five and usually less. Other characters are designated by roles: the sister, the landlord, the stage manager, etc.
Self-publishing eliminates the need for a synopsis for querying, but it can still be a good plotting tool. Writing out a synopsis can show up your plot holes and shape up your story line, so I'd recommend writing one, even if you never need to show it to anyone.