For answers, click on the link on "answered" below the post. The first part is the number right after "physicsoverflow.org/", e.g. 4551, and the second part is the part after the "#" at the end of the URL, including the "#" itself, e.g. "#a4758". Combine the first and second parts, e.g. "4551#a4758". The same holds for comments, but the code will look like "****#c****" instead of "****#a****".
For short tag wikis, input it as tag/TAGNAME,e.g. tag/string-theory.