Or I could just write one here?
Basically, dispersion is in minutes of arc (roughly fifteenths of the previous measurement, so everything looks larger but shouldn’t be Less Accurate). Sight-dispersion is the sights being imprecise, and the main dispersion is the gun itself. Ammo affects that as well. Dispersion moves your shot away from your aim point, and your skills (weapon/marksmanship) counter that.
Hitting “f” or whatever key you’ve got set for gun use brings up the weapon, and you point it roughly at the tile in question. In order to actually use the sights and aim (making sure that pre-dispersion aim point is on the target), you use the various keys there to spend time on the shot. As you do, the Steadiness bar fills, and you should see some improvement in the Confidence bar.
Confidence key (the more symbols, the greater the chance):
- = relative chance for a crit/headshot
- = relative chance for a good hit, center-mass sort of thing
| = relative chance for any hit, may or may not damage through armor
The confidence bar is not itself very confident, by design, so it’s pretty safe to presume that if it thinks you have good odds, you do.