Rogues can sneak attack defenders that they flank.
Most ranged weapons can't be used while the attacker is prone, but a combatant can use a crossbow while prone. A ranged attack gets no special bonus. If a combatant wields a second weapon in the off hand, that combatant can get one extra attack per round with that weapon. A light weapon is one that's smaller than a weapon a combatant could use in one hand. Its size category is smaller than a combatant's.