A check is a test to see if your innate talent and training are enough to overcome a challenge. Most of the time, you must make a check because the DM has determined that an action you want to attempt has a chance of failure. The outcome is uncertain, and your DM turns to the dice to determine your fate.
When you need to make a check, your DM asks you to make the check using an ability of his or her choice. The DM chooses the ability that applies best to the task at hand.
Making a Check
To make a check, first refer to the ability on your character sheet. The ability has both a score and a modifier.
Roll the Die: To make a check, roll a d20 and add the relevant ability's modifier.
Apply Bonuses and Penalties: If a class feature, a skill, a spell, or some other effect gives you a bonus or a penalty to this check, apply it to your current total. Some bonuses and penalties apply to all checks made with a particular ability. Others apply only under certain circumstances.
Announce the Total: Tell the DM the result of your check
When you make a check, your DM picks a Difficulty Class (DC) for the check. Your DM has details on how to determine DCs. The more difficult a task, the higher its DC.
If your check result is equal to or greater than the DC, you succeed. Otherwise, you fail. When you succeed, your action works as intended. When you fail, you either make no progress or perhaps suffer a setback as determined by the DM.
A contest pits two characters or creatures against each other, with success determined by each contender's luck and talent. Contests function like checks, with one major exception: instead of matching your roll against a DC, both you and the person you are opposing make a roll. You then compare the two results to see who succeeds.
When to Have a Contest: Contests arise when two creatures attempt to do the same thing and only one can succeed, such as if both you and a bandit attempt to grab a magic ring that has fallen on the floor. In other cases, you might attempt an action that another creature actively opposes. If you attempt to push open a door that an orc holds shut from the other side, you make a check to open the door, and the orc makes a check to keep it shut.
Resolving a Contest: A contest uses the same rules as a check, except that two creatures each make a check. Any bonuses and penalties you apply when making a check with an ability also apply to contests involving that ability.
The creature with the higher check result wins the contest. The creature either succeeds at its action or prevents its opponent from succeeding.
If there is a tie, neither creature succeeds. The situation remains the same as it was before the contest. This might allow one creature to win the contest by default. If you and a bandit tie in a contest to grab a ring, neither of you grab hold of it. If you tie in a check to push open the door held shut by on orc, the door does not open. In this case, the orc prevents you from opening the door even though it did not win the contest.
When you meet a ferocious monster, you likely will need to attack it to defeat it. An attack roll is similar to a check, except that the die roll is not against a normal DC. Instead, you compare the result of your attack roll to your target's Armor Class (AC). To hit the target, your result must be equal to or greater than the AC. If you hit, you deal damage with your attack, reducing your target's hit points. When a creature drops to 0 hit points or fewer, the creature typically falls to the ground, dying.
Additional rules for attacks and taking damage are provided in the Combat section.
A saving throw represents a desperate attempt to resist a spell, a trap, a poison, a disease, and similar threats. You make checks and attacks when you decide to take an action. You make saving throws in reaction to events that happen to you.
Making a Saving Throw
When your DM asks you to make a saving throw, he or she will tell you what ability to use to make the saving throw.
Roll the Die: To make a saving throw, roll a d20 and add the relevant ability's modifier.
Apply Bonuses and Penalties: If a class feature, a spell, or some other effect gives you a bonus or a penalty to this saving throw, apply it to your current total. Some bonuses and penalties apply to all saves made with an ability. Others apply only under certain circumstances.
Announce the Total: Tell the DM the result of your check.
Saving Throw Outcomes
When you make a saving throw, the effect you attempt to resist has a DC. Powerful effects have higher DCs, while weaker ones have low DCs.
If you fail the saving throw, you suffer the full force of the effect you attempted to resist. A spell might inflict its damage against you, you might fall into a pit that opens beneath you, or a poison might sap your vitality.
If you succeed on the saving throw, you either avoid the effect or suffer a diminished version of it. You might take cover and suffer only partial damage from a spell. As a pit opens, you might leap to solid ground. A poison might cause you to feel ill, but you are durable enough to shrug off some of its effects.
Advantage and Disadvantage
Sometimes, you have an edge in a situation. A magic item might grant you a burst of strength for a check, an enemy might be unaware of your attack, or your cloak of fire resistance might absorb much of a fire's heat. In such situations, you have advantage.
Other times, circumstances conspire against you. An evil cleric's vile curse might interfere with your attack. Some magical effect might attack your mind, thwarting your concentration, or you might try to attack while hanging onto a cliff face. These are all situations where the odds are against you. In such situations, you have disadvantage.
You usually gain advantage or disadvantage through the use of special abilities and spells. Your DM might also determine that circumstances are in your favor and grant you advantage, or that they are not in your favor and impose disadvantage.
If you have advantage or disadvantage on a check, an attack roll, or a saving throw, you roll a second d20 when making that roll. You use the highest roll between the dice to determine your result if you have advantage and the lowest roll if you have disadvantage.
No matter how many times you gain advantage or disadvantage on the same check, attack roll, or saving throw, you roll only one additional d20. If you have advantage and disadvantage on the same check, attack roll, or saving throw, the advantage and the disadvantage cancel each other out for that roll.