If this question has already been asked I couldn't find it. On the DB it seems to describe super effectiveness as double damage and ineffectiveness as half damage. Is that a literal representation of what the damage bonus is?
Super effective moves are 2x damage.
'Reliable source' as you requested... http://bulbapedia.bulbagarden.net/wiki/Super_effective#Super_effective
Super Effective means double damage, or x2. You do twice as much damage. Like... Super Effectiveness:252 SpA Life Orb Greninja Hidden Power Water vs. 252 HP / 4 SpD Heatran: 205-244 (53.1 - 63.2%) -- guaranteed 2HKO Normal Effectivness:252 SpA Life Orb Greninja Hidden Power Dark vs. 252 HP / 4 SpD Heatran: 103-122 (26.6 - 31.6%) -- guaranteed 4HKO 26.6 - 31.6% is for normal and 53.1 - 63.2% is for super effective. See how super effective is 2x as much damage as normal? It does twice as much. I am doing not very effective for your convenience, Not Very Effective:252 SpA Life Orb Protean Greninja Hidden Power Psychic vs. 252 HP / 4 SpD Heatran: 51-61 (13.2 - 15.8%) -- possible 7HKO 2x less chance to KO than Normal Effectivness, except for that 7HKO, but see? It does half damage.
Hope I helped!
Yes, it is double damage. Source: Experience
Yeah. Simply it just doubles the damage that you do.