Right, that's done!
First of all, I'd suggest you start with something shorter than the word limit allows -- say 600-800 words, perhaps. That's plenty for us to see what's going on with your writing, and give general advice. Once you've got the first one under your belt, and you've applied whatever is suggested, then you can put up longer pieces as necessary -- but the longer the extract, the fewer critiques you're likely to get.
Second, I'd say post something where you need help. It's often easiest to give the opening scene, as we'll be coming to it fresh as any reader would, so you don't need to give explanations as to who people are and what has been happening. If there are things that need sorting out in your writing, then they're usually obvious from the start, so whatever is said, you can then apply to later scenes.
But if there's a particular scene which is worrying you, and it comes from the middle of the book, then give a bit of scene-setting eg "We've seen Fred leave the militia, and we know he's in love with Bert, but this is the first time we see them together." Sometimes things make sense only in context, so if there's something in the piece which is odd, explain that eg "We've already seen that blackened teeth are seen as desirable."
And yes, what we'll be looking for is how you tell the story -- whether your prose is grammatical or it's overwhelmed with adverbs, if you're using POV well, if description is flat, or you're info-dumping. The actual story isn't something that we can worry about at this stage.
And before putting something up, do read around the pieces already up. Critiques can seem to be brutal, so check out what people say and how they say it, and prepare yourself. And when you put something up, just remind us this is your first time and ask us to be gentle -- most people will give you slack if you ask for it. After reading the comments, don't feel the need to respond at once, particularly if you're upset. Just thanks the critiquers and leave it at that.
One other thing, if possible, avoid putting up work which you've only just started -- better yet, don't put anything up until the whole first draft is finished. If the critiques are upsetting, you might get too discouraged to return to the work if you've not got far along with it.
