How can I create a workflow in Confluence?
There are a number of add-ons that provide workflow and review capabilities such as Comala Workflows under a commercial licensing, while others, such as the Page Approval, are the free or open source.
Comala Workflows adds the ability to moderate content before it gets published in Confluence. With it, you can select multiple reviewers, create a workflow for page approval and assign tasks for a specific page as you follow it through to publishing. Refer to Comala Workflows documentation.
A more informal way of performing document acceptance without using add-ons is to use page restrictions. With page restrictions, you can create an initial page, restrict the view of the page to only the editor and approvers, then remove restrictions and open it up to a wider audience once the necessary edits/approvals have been made.
For attachments, Arsenale Lockpoint will add file check-in and check-out features while Confluence already versions attached documents natively.