Most uncertain actions in Risen Kings use the same basic pattern:
Roll a d20, apply the relevant modifiers and any Boons or Banes, then compare the total to a target number.
If the total equals or exceeds the target number, the roll succeeds. If the total is lower, the roll fails.
The modifier and target depend on the type of roll. Ability Checks usually add an Ability modifier and are compared to a Difficulty Class. Attacks usually add an Ability modifier and Proficiency Bonus and are compared to a defense.
Specific rules may change what is added, what value is targeted, or what happens on a success or failure.