Accuracy increases chance to hit with melee and ranged weapons (not spells).
Chance to Hit = Attacker's Accuracy / ( Attacker's Accuracy + (Defender's Evasion / 4) ^ 0.8 )
Evasion (not to be confused with dodge) is the stat accuracy is weighed against, as in the formula above, and if hit it is also used to lower the chance of being crit. It likewise does not affect spells. (Many Dex-related characters have easy access to movement speed increases though, which can aid in avoiding spell and other types of damage.)
Dodge (obtained only from passives) works simply as the passives that grant it suggest. Acrobatics gives a 20% chance to dodge non-spell attacks, and Phase Acrobatics grants a 20% chance to dodge spells.
Block also does not work for spells, unless certain spell-blocking passives are obtained. Blocking can be done with a shield, staff, or dual-wielded weapons. When dual-wielding, the base block chance is 15% no matter the weapons used. If a blocked attack would have caused a stun, a block animation plays (sort of stunning you anyway), which can be shortened through block recovery.
Armor and Resistances prevent physical and magical damage, respectively. Armor reduces damage from physical hits in flat amounts, making it worse against higher-damaging hits, whereas resistances are applied in percentages (capped at 75% - which can be raised through certain affects). Your resistances are lowered in higher difficulties (-20% in Cruel and -60% in Merciless).