Zotero offers word processor plug-ins that allow you to create citations and notes within your document. See the next section for Plug-in specifics.
Zotero offers a convenient drag-and-drop, or Quick Copy, method of creating a bibliography from items in your library. Simply select an item from your library in the middle column, and then drag it to a text box or word processor document. These items will appear as a bibliographic citation arranged in alphabetical order.
You can change citation format by clicking the gear icon in Zotero and selecting Preferences. This reveals a dropdown menu with not only citation styles but also preferred export formats.
For more information, see Zotero's creating bibliographies page.
Currently, Zotero cannot import items from bibliographies in text documents.
One solution to this is if you have these items saved in a bibliographic database. Export the items to an intermediate format, such as RIS or BibTeX, and then import them into Zotero.