for ($1;$2;$3) { `yas-selected-text`$0 }

M-x yas-visit-snippet-file, key binding: C-c & C-v Prompts you for possible snippet expansions like yas-insert-snippet, but instead of expanding it, takes you directly to the snippet definition's file, if it exists.

M-x yas-new-snippet, key bindind: C-c & C-n Creates a new buffer with a template for making a new snippet. The buffer is in snippet-mode (see below). When you are done editing the new snippet, use C-c C-c to save it.