If you just want to quickly add references to a paper, email, or blog post, Zotero's Quick Copy is the easiest way to go. Simply select items in the center column and drag them into any text field. Zotero will automatically create a formatted bibliography for you. To copy citations instead of references, hold down Shift at the start of the drag.
You can also use Quick Copy keyboard shortcuts to copy citations and bibliographies to your system clipboard and then paste them into documents. Default shortcuts are Ctrl/Cmd-Shift-C (bibliography) and Ctrl/Cmd-Shift-A (citations).
To create a bibliography or a citations list in Zotero, highlight one or more references and then right-click (or control-click on Macs) to select “Create Bibliography from Selected Item(s)…”. Then select a citation style for your citation/bibliography format and choose either to create a list of Citations/Notes or a Bibliography. Then choose one of the following four ways to create your citation/bibliography: