Okay, this isn't what most people are saying, but I think it depends on your goal at the moment. Do you intend to submit your current work? Or are you still just working on getting the hang of it and doing it for fun? If it's the latter, there's not much need to show anyone yet.
I would recommend letting someone else see it, however. Preferably someone who understands. The truth of the matter is almost all of us sucked the first time around. A lot of us suck the third or fourth times around. Please try to understand that no matter how much of yourself you put into your story, a critique is not a personal critique about
you. Your worth as a person is not defined by whether or not someone likes your manuscript. Might sound hard to believe, but it's completely true.
Anyway, take me for instance. Even if you showed me something that was very poorly written, I'm not going to say, "Wow you should just give it up, you're hopeless and pathetic." Now, I
have met people like that, and those aren't the kind of people you want to be around. The purpose of a critique is to offer points of improvement and let you know what's working. I'm not going to look down on you if your work is still in the newbie stage. All of us were there once, and I know that you will improve over time. A lot of us are going to be like that.
And think of it this way. Even if it needed a lot of work, it's often hard to understand what exactly it is that needs work. Say, for instance, you use a lot of passive verbs. Maybe you don't notice that (I used to do this all the time and have just gotten to where I fix them on my own), but someone else would, and that person could say, "You use a lot of passive verbs. Try wording it more this way..." That gives you something to go back and look for yourself, and then you'll be more aware of it when you write next time, and thus will improve.
So really, not all that much reason to be afraid. Posting online is scary, but find a writing buddy who can read through a bit and just offer you pointers to begin with. Everyone is nervous about it, but it really isn't that bad, and it might be one of the best tools you can have.
On the other hand, having said that, if you really are nervous and feel that your work has lots of basic errors, etc. that you want to learn how to fix beforehand, do some searches for writing tips and start checking your manuscript, or check out a writing book at the library. Once you start getting more confidence it won't seem quite so scary.