Mouse Speed controls how fast the Circle Pad or Touch Screen moves the mouse. If set to 0 and using the Touch Screen, it will set to the absolute position, rather than moving relatively to last position,
Buttons can either be a letter for example B, or a special key, like SPACE, CLICK, RIGHT CLICK, ENTER, BACKSPACE, SHIFT, TAB, LEFT, RIGHT, UP, DOWN, PAGE UP, PAGE DOWN, or WINDOWS,
Throttle controls the delay between checking for new packets (in milliseconds), a high number will have slightly more lag between pressing a button on the 3DS and receiving it on the PC, however will make the application use less CPU. In my experience, 20 is a reasonable throttling amount,
Make sure to use a single space, not a tab for seperating settings,