The Core Mechanic
To determine if your character succeeds at a task, you roll a ten-sided die. A roll of 10 is not an automatic success, nor is a roll of 1 an automatic failure.
Compare your result to a target number (“Difficulty Value”, or DV, when making a skill check or saving throw, and “Armor Value”, or AV, when making an attack). If the result equals or exceeds the target number, your character succeeds. If the result is lower than the target number, you fail.
Dice rolls are described with expressions such as “d+5,” which means “roll a ten-sided die and add 5” (resulting in a number between 6 and 15). The first number tells you that a die is being rolled. Any number after that indicates a quantity that is added or subtracted from the result, which is called the modifier.
Taking 5 and 10
It doesn’t always make sense for actions to carry a random element. When you are not in any danger or otherwise distracted, you may “take 5” – treat a roll as a 5 (the average) instead of rolling, to represent an average result. If you have lots of spare time, and the action you are attempting carries no consequences for failing (such as straining to open a tight jar) you may treat the result of the roll as a 10, but doing this means that the action takes 10 times as long as normal. In effect, it’s assumed that you’ve rolled the die 10 times until an actual 10 came up. Ultimately, the GM decides when you are permitted to take 5 or 10.