Distance and angle are the means of detection of gaps in raster toonz.
To fill the gaps, distance will detect the gap between two ends of a gap according to the set distance and angle will fill the gap according to the set angle setting. So if you want small gaps only to be taken into account, you need a small value and vice versa.
If you only want gaps of a certain angle to be taken into account depending on your setting. You have to modify angle setting.
Opacity only affects the color. The higher the value, more the line is visible and vice versa.
you can enter the index of the style you want to use as join by using the numeric keypad (1,2,3 ...) from the index style.
The normal mode takes into account all the detectable gaps. And the others according to the zone defines.
Before closing the gaps I advise you to activate "gap check" in the view menu and then change the angle and distance setting to see which gaps will close more intuitively.
the finger tool is used to fill very small pixels that can remain in a coloring process with toonz raster. It automatically detects the index of the color and allows drag that color.