The value used for the Evade check is determined by adding the investigator's net Sneak skill value with any special Sneak or Evade adjustments they may have from Skills, Allies, or other cards, and finally adding or subtracting any special adjustment for this check. This total gives the number of dice used for the Evade check.
Normally passing the Evade check requires only one success.
Evade Checks against Monsters
To succeed in the Evade check against a monster, an investigator must roll at least one success. Any roll which fails to make the necessary number of successes is a failure, and the investigator must take stamina damage from the monster's attack (barring any special abilities which enforce different rules).