I'm building a website where users contribute original content to a collaborative story writing process. I assume since they are submitting it to such a site, they are implicitly giving me the right to display said work on the site. I understand that I cannot claim copyright ownership of said work, but for example, when I make a post on Reddit, Reddit doesn't own the content I wrote, but yet they are still permitted to display it to all other users who visit their site. Since I own the copyright to my own work, do I have the right to send Reddit a take-down notice for my own work (assuming I didn't already have the ability to delete my own post)? Could users do this to me on my site?
I would eventually like to be able to use this user-generated content on my site for other purposes, all expressly related to or in the context of my site (e.g. publishing a compilation of user-generated work from multiple users, either for free or at-cost). Is this in any way possible without some process of getting legal documentation from every user of my site?
In short, is there any way to enforce that original content posted to my site shall be covered by commercial-use-allowable Creative Commons or other such licenses, effectively making them public domain or something like that? I understand that I'm throwing some of these terms around a bit without really using them correctly. I don't know anything about legal stuff, this is a hobby project and I basically just don't want to get myself into trouble.
It's already on my radar to provide an avenue for owners of copyrighted material to send me take-down notices if they find that a user of my site has posted their content without permission, but when a user posts their own original content to my site, I want to know what I am allowed to do with it.