A GatherContent project consists of a number of items (or content pieces), which you can find on the Content tab. The items can be organised into a hierarchy to reflect a website's sitemap, which can be re-ordered at any time.
An item has a structure applied to it, and this structure contains the fields which you can enter content into. A structure and a template are the same thing, but a template is a saved structure, which can be quickly and easily applied to other similar items.
As you're writing and editing your content, you'll notice that the content is regularly being autosaved. You can restore these revisions later if you need to restore a previous version of the content.
You can leave comments on content and assets, which you can notify others of, and start a conversation around any changes that might be needed.
A person can be assigned to an item. When this happens, they're effectively responsible for it, and get included in item updates such as workflow status changes and upcoming due dates.