Could someone explain how this whole posting thing works? If I post, say, a short story for critique, am I basically giving away that work? How does copyright work with unpublished works posted online, where anyone in the whole world can view it? Can I have that work published later? I'm sorry, this is probably a pretty 'duh' kind of question but I don't have that much experience with internet things. Most of my pre-college writing was done on a typewriter.
Howdy, I've heard that posting it publicly does count as publishing. You are better off, probably, sending it to people to review privately. If you can't find volunteers on here, you could try the Facebook group I use: https://www.facebook.com/groups/betareaderconnect/ Also, just searching on twitter for #betareader works pretty well.
We have an FAQ entry partly dedicated to this: https://www.writingforums.org/faq/does-the-workshop-harm-my-chances-of-being-published.101/. In short, it may harm your chances of getting pieces posted here picked up by publishers later. However, it can probably vary from case to case depending on publisher's rules (e.g. our Workshop cannot be access by anyone without an account and this might affect how publishers view it). Also, as is noted in the Forum Rules: When you post something for critique in our Workshop, you grant WF limited use of your story. More specifically, other members may quote your piece (in part or in full) in their replies to the thread, and only the staff may decide if a thread should be deleted or not (and we generally don't delete anything). So, you still own the copyright of your work -- you're just granting the forum staff and user base limited use of it. If you have a story that you treasure very much and want to try to get published in the future, it is safest to keep that story private (e.g. get private critiques as suggested by @John Calligan) and instead write other stuff in the same genre/similar setting/whatever to post for review in the Workshop.