Just a few quick notes as I'm busy doing other stuff to write this guide up.
The applet is (should be) intuitive enough to create and play Su Doku problems straight from the newspaper. Just open it up and have a bash.
|Position||A unique board location|
|Fixed||Make a position non-modifiable|
|Group||A row, column or grid|
|Grid||An inner box of values|
|Value||Typically the numbers from 1 to 9 inclusive|
|RMB||Right Mouse Button|
|MMB||Middle Mouse Button (where available)|
Unlike other programs, you keep clicking (left mouse button) on the same square to get it to change to a different value (or none at all). What values appear will depend upon some of the options you may have selected (i.e. Placement Assist). Some positions will not be changeable (aka fixed, non-modifiable) and have a grey background.
Seeing as a web browser hosts this applet and requires its own handling of the keyboard and mouse, things can go awry. If you're having troubles with getting key presses to work, click about outside the playing area (but within the applet) and try again.
Here things get weird.
As a preference over pencil-marks (candidate drawing) and from playing Rays from Hoyle Puzzle Games 2005, I've implemented a flagging/highlighting system. When playing on good ol' pen and paper, using your finger is handy to mark or discard a group. Here I've emulated this with a saturated yellow background when you use these keys:
|Arrows||Highlight the position from where the pointer rests in the direction of the arrow|
|Shift||Clear all highlights|
|Enter||Highlight the grid under the pointer|
|Ctrl||Highlight all intersecting rows, columns and grids|
|RMB or MMB||Toggle the highlight under the pointer|
Now, if you do like pencil-marks, you may enable them via the Action menu.
|1, 2, ..., 0||Remove the specified candidate in the position from where the pointer rests|
|Backspace||Remove candidate changes in the position from where the pointer rests|