Cite all quotes and cites every remaining matched passage at once, in the style you have chosen.
What happens
Each open plagiarism card is resolved as if you had chosen Cite on it: the matched words are quoted, an in-text citation follows, and each distinct source is added to the reference list once. Cards you already ignored are left alone.
When to use it
When your matches are genuine quotations that you simply forgot to cite, Cite all finishes the job in one step. When some matches should be rewritten instead (for example a passage you meant to paraphrase), resolve those cards first and then use Cite all for the rest.
Undo
Cite all is one step in the undo history. Undo removes every citation it added, together with the reference entries.
Sources without details
A source with no author, title or date is still cited; the citation uses the page title, or a shortened form of it, and n.d. where a date is missing. Review those entries in the reference list before you submit.