Whenever possible, a Ranger’s actions should be resolved by its player simply describing what the character does, followed by the GM revealing what happens next. This keeps the game moving at a nice, fluid pace.
However, if the action is risky, the GM may call for a check. Whenever a check is required, the GM determines the difficulty: Challenging (13), Hard (15), or Very Hard (17), which determines the number the Ranger needs to surpass in order to succeed on their check.
The player controlling the Ranger involved in the check rolls a d20 and adds the relevant ability bonus, as determined by the fiction. If the total is greater than the difficulty number (13, 15, or 17), the character succeeds and play resumes as normal. If not, the Ranger fails and the GM describes how things go wrong or go from bad to worse.
Sometimes the GM might call for a saving throw in order for a character to avoid harm or other undesired consequences. The player rolls a d20 and compares it to the ability defense relevant to the narrative. For example, nimbly dodging out of the way of a trap might call for a Dexterity saving throw. If the result is less than the ability defense, the character successfully saves. If not, the GM introduces harm or a consequence.
Usage Dice know the following tiers: D8>D6>D4>D2. It decreases on a 1-2. A D2 means you can use it one final time.