With yank commands you can put "<a-zA-Z> before the command, just as with delete commands. Otherwise you only copy to the undo buffer.
* | y<move> | Yank from begin to endpoint of <*><move>.
* | yy | <*> lines.
* | Y | Idem (should be equivalent to `y$' though).
- | m<a-z> | Mark the cursor position with a letter.