A block quote is a quote that is long enough (at least 4 lines of prose or 3 lines of verse in MLA; at least 40 words in APA) that it needs to be set off from the rest of its paragraph to help it stand out to the reader. Some important formatting rules to know are that
every line of a block quote is indented a half-inch further in than the rest of the paragraph it's in,
it does not use quotation marks, and
its citation is outside of the period of its sentence.
For an example and more information, please see the last example in the linked handout: