Evasion

Evading an attack prevents all damage and other harmful effects from the attack. Only attacks and attack skills can be evaded. Spells cannot be evaded.

Blocking
Blocking an attack prevents all damage and other harmful effects from the attack. Usually, only attacks and attack skills can be blocked, but there are some passive skills that allow you to block spells.

When an attack is blocked, the game first calculates if the attack would have caused a stun were it not blocked. If it would have caused a stun, the blocking animation is played, stunning you briefly. If it would not have caused a stun, then you get a "free" block with no animation. Faster Block and Stun Recovery and Increased Block Recovery modifiers reduce the length of the blocking animation.