I've seen a couple writers use this "--" in their writings; what does it mean? I don't have an examples. I would do a simple google search on what it means, but I don't even know what it's called to do so.
It is a substitute for an em dash.
When an em dash is unavailable in a particular character encoding environment—as in the ASCII character set—it has usually been approximated as a double (--) or triple (---) hyphen-minus. The two-hyphen em dash proxy is perhaps more common, being a widespread convention in the typewriting era. (It is still described for hard copy manuscript preparation in the Chicago Manual of Style as of the 16th edition, although the manual conveys that typewritten manuscript and copyediting on paper are now dated practices). The three-hyphen em dash proxy was popular with various publishers because the sequence of one, two, or three hyphens could then correspond to the hyphen, en dash, and em dash, respectively.