Controls
The row of three square buttons operate the Start, Stop, Lap On & Off, and Reset. As you mouse-over each button their name is displayed.

The first press of the green button starts the countdown, it then turns red. Pressing it again causes the countdown to be stopped (paused). A further press and it will resume counting.

Once a countdown has begun the Lap (orange) and Reset (yellow) buttons become active. The first press of the Lap button displays the current lap time. Pressing it a second time hides lap time and returns to the countdown.

Clicking Reset cancels the countdown and returns you to the start time.

Front edit mode
Click on the hours, minutes or seconds to enter edit mode and click again to exit.
Change the value by using your mouse scroll-wheel (or trackpad if you have scrolling activated).
Or press the Tab key to activate editing Hours, Tab key again to switch to Minutes, again for Seconds, and again to deactivate editing.

Also when edit mode is activated you can either type the number directly or use the + and - keys to increment/decrement. (3-2-1 expects two numbers to be input when typing them in, so for 2 minutes you would enter 02).

Preferences
The i button flips the widget to show the preferences on the back. Here you can enter the Hours, Minutes and Seconds you wish to countdown from - by either using the popup lists or typing directly into the input fields.

Tab between the preference fields (For complete keyboard navigation - open popups and move with the arrow up/down keys. The Enter key selects an entry and closes the popup).

The Notifications preferences enable you to bring Dashboard to the front and the countdown has finished. Also you can enable an alarm sound, with or without repeat, to play when the countdown has finished.

The alarm sounds popup lists all the sounds in the Library/Sounds folders. If new sounds are added to these folders, 3-2-1 needs to be reloaded in order for them to show up in the list (Cmd-R).

Each running countdown has its own label (up to a maximum 46 characters) - to help with identification if you have more than one countdown running.

The Notification settings and Alert message and Label text may be changed while a countdown is in progress, i.e. they take effect immediately on the current countdown.

Clicking on the Done button returns you to the front of the widget
(or press Enter or Return to apply any changes and return to the front).
The Help (?) button brings you directly to this page.

Resizing
Click and drag the resize handle on the front bottom right of 3-2-1 to resize it.

Updates
3-2-1 automatically checks for new versions at startup (only the version number, and no personal information is being sent). If a new version is available an 'Update available' badge will appear on the front of the widget. You can either dismiss this badge or click on it to download the latest version.