If an adventurer is trying to accomplish something, like sneaking up on a Goblin, or lifting a heavy object, they need to make an ABILITY CHECK.  

The Game Master

The Game Master determines how difficult the task will be, then gives the adventurer the number to beat on a 20-sided dice.

10  for mostly easy
15  for kinda hard
20+ for very challenging 

The Adventurer

The adventurer rolls a 20-sided dice and then adds their ability bonus. If they roll the Game Master’s number or higher they succeed! 

The Game Master tells the adventurers the appropriate ability score for the task. For instance Use DEXTERITY for sneaking up on the Goblin. Use STRENGTH for lifting the heavy object.

If the character is proficient in the right ability, using STEALTH for sneaking for example, they will have a higher bonus listed on their character sheet.