synopsis is a brief (think one paragraph) description of your story. It establishes the major characters and the problem/"hook" of the story. (i.e. What's the conflict, why would the reader care?)
A logline is a tagline, a one sentence, compact, manageable synopsis to give to guys with a tight schedule. It's an infomercial in less than 25 words. It gives the main character and problem in a rapid fire "bullet" explanation.
Note that both of these should suggest the mood of the story (comedic, tragic, strange, etc.) and also hint at the theme (love, war, peace, and all that other touchy-feely crap. ;) )
But seriously dude, eHow or wikipedia can help you out if you don't know something. (And save my poor, typed-to-the-bone fingers)
More importantly, no one is going to take you, or your story seriously if you don't have a grasp on some of the basic tools of the trade to narrative writing. Being a newbie is fine, everyone's gotta be a noob at least once, but that's also what a library is for. You should grab some books on the subject, read up to attain knowledge, and then tote it around, spouting off concieted bits of wisom at random intervals. (Like me)
People who calculate a lot are usually the ones who don't make it big in the comic/manga industry, Sad but it's true.
The question of "why would the reader would care?" isn't easy to know, cause different types of people will read through it, mostly children but adults as well.
So no matter how cool you think your comic is, if majority(and not just majority but just majority of people who pick up your book or read it online which you really "won't know who") doesn't see it good then it'll never be considered good.
Adults are the ones who read the book before it's published, So they might base it on how AnimeRebel says, but in my opinion just do it on what you want other than thinking too much of advices from other people, and saying "this is how you should do your story"
If they're editor publishers, however. then you can't do anything but to obey.
As for you being afraid to show your story, you shouldn't. TBH if some editor guy stole my story then I'll be proud knowing they published my story and other people are reading it and "not just stuck in my mind forever!"
You shouldn't be afraid of us here who might steal your story cause those who steal are mostly editors which you'll be showing your story if you're applying for a job, life is a gamble but if you're afraid to step on the streets to buy some milk cause you're afraid to be run over by cars-- well... you get my point.
Head on over to the Roleplayers & Writers Arena and Manga & Anime Works section. There's a bunch of folks who're sharing their work. Maybe you'll get help, learn a few more things, and even get ideas. :>