A log line (most commonly used for movies) is one sentence that describes your book. Think of a movie poster. For example, for one of the Jaws movies their log line was: Just when you thought it was safe to go back into the water... Now you can do something like this or you can make a comparison. When I first saw the book The Selection by Kiera Cass it was always described as: The Bachelor meets Hunger Games. Sometimes those who want to hear or see your log line will give you a word count to stay under.
A pitch can be a little more flexible. Sometimes a pitch can be one sentence and other times (if the person you are pitching to says so) it can be longer. They may give you a line limit (like 3 lines) and a word count to stay under (in my contest it was under 25 words). A pitch needs to cover your main character, the major plot, or, what's at stake, and end with the reader wanting to find out more.
I worked on it for a few hours and for my novel I am Caraway, I came up with this:
5 word log line: The real reason faeries vanished.
25 word pitch: In the year before the Norman Conquest, one girl, in love with the faerie prince, learns she is fated to save mankind from faeries.
Well, I ended up not winning ): But that's alright. Savvy Authors has plenty of pitching opportunities going on all the time so I'm sure I'll enter another one again soon. Here's a link if you're interested: http://www.savvyauthors.com/vb/content.php
Hopefully this helped you a little if you're trying to figure out pitches and log lines. They can be tough, trust me! It's really hard to sum up your book, especially if you've never had to before. But when you go to writer's conferences these are things you'll need to have handy. Plus, if you get lucky enough to find representation, your literary agent has to use things like log lines and pitches in order to get editors interested in your book and hopefully buy it. So, pain in the butt they are it seems they're also a necessary evil in the world or writing.
Good luck! Feel free to comment below and check back again soon for more tips and reviews!