Add your own tags or use / edit the tags that are imported when you save an item. You can also use color tags to help visually organize your library. HINT: Drag an item to a tag in the tag selector and the tag is automatically added to the item.
Related items allows you to set up a relation between any pair of items in your library. Check out the third-party plugin Zutilo that helps you organize tags and related items.
Group libraries are separate from your personal library.
or go to https://www.zotero.org/groups/ and select Create a New Group.
Share your own work using Zotero. My Publications allows you to quickly share a bibliography of your work. You can link your publications to your Zotero profile (see Shannon's as an example). You can also share files for which you have distribution rights.