If you need only one tile to go out, you have a ready (or calling) hand.
If either of the ready hand rules (obligatory or voluntary) is enabled on the Ready rule option page under the Rules section in the category tree of the Preferences dialog box, the condition of being ready must/can be declared, i.e., a player informs on his own turn that he needs only one tile to go out. When a player declares ready, a sound is heard, and the color of his name (appearing in the claim column and Players window) changes.
Note: After you have made the declaration, the caption of the command button changes to read "Out". A player cannot declare a Kong immediately after the declaration (but it is allowed on the subsequent turns). Normally Four Winds does not validate an obligatory ready declaration, but validation can be turned by checking the Validate the declaration box on the Ready rule option page of the Preferences dialog box.
Note: A player cannot declare a Kong immediately after the declaration (but depending on the rules, it may be allowed to declare a concealed Kong on the subsequent turns). Depending on other options chosen the tiles in the hand may be turned face down and/or locked as soon as you make your next discard. Notice too, that the rules may require that the hand must be completely concealed (concealed Kongs are allowed, though) in order to be declared ready. There are also several other optional restrictions for declaring ready. For details, see Rule Variations Voluntary Ready declaration.
Declaring a Kong
Obligatory Ready declaration
Voluntary Ready declaration
Ready on original hand
Ready on first turn