Nearly everything you do in the community is about collaboration. Content you add is usually visible and searchable by everyone (unless you've expressly indicated that its visibility should be limited to certain people). Other people read your work, you read theirs. You get ideas from someone else's blog, they comment with suggestions on your document.
But you can manage collaboration and access to content. For example, you can say that only certain people are able to edit the document with you. You can also specify that certain people must approve it before it's visible to everyone.
Limit to certain collaborators. When you first create a document, you limit its visibility by setting its collaboration options. When you add people to edit and approve a document, you're giving them special roles in what's called the document's "workflow." In other words, work on the document starts in one place — a draft — and moves through a process — possibly more drafts, review, and approval — until it's ready for publishing.

After you've saved the document, you can come back later to edit these options by clicking the Manage Collaboration link in the Actions list. The people you added to edit and approve the document will be able to get to this document from the Notifications tab of their their own profile.
The document itself will also let approvers know that it's time to approve.
