DnD 5e - Dice
Dice are a core component of the game. Once you have a set of dice and understand how they work, you'll understand how they work in nearly every RPG except for those which include custom dice like FATE or Fantasy Flight Games' Star Wars RPG.
A typical set of dice can be purchased as a matched set from any local game store, a hobby shop, or a comic book store in some places. You can also find dice sets online from a variety of retailers at a variety of price points.
Dice are identified by their number of sides (d#), so a die with 4 sides would be called a "d4". The "d" is always lowercase, though I'm not certain why. Gaming dice typically have engraved numbers instead of "pips" like the dice you might find in a game like Monopoly.
- d4: A d4 has 4 triangular faces in the shape of a pyramid. The d4 can be somewhat difficult to read because each face features 3 numbers. When rolling a d4, wait for it to come to rest flat on the table, then read the number which is upright. The other numbers will be upside down at an angle. Don't step on these.
- d6: The most common die, the d6 has 6 square faces and can be found in any familiar board game, such as Monopoly or Yahtzee!. Many characters find that they need to roll several d6s for the same actions, so it is often smart to have a few extras handy.
- d8: The d8 is a diamond-shaped die with 8 triangular faces.
- d10: The d10 looks a bit like a rounder d8, and features 10 roughly triangular faces with one rounded edge (roughly a teardrop shape). A d10 has numbers from 0-9; the 0 represents 10, but uses a single digit because engraving 2 digits can throw off the weighting of the die.
- d100: The d100 is shaped the same way as a d10, but features 10 numbers which each have a trailing 0 (00, 10, 20, etc. up to 90). These are used for rollinga d100 (also called a d%, a.k.a "d-percent" or "or d-percentile"). When rolling a d100, roll the d100 die for the "tens" place of your roll, and roll a d10 for the "ones" place. If you roll 00 on the d100 and 0 on the d10, you have rolled 100.
- d12: The d12 is typically the largest die in the set, and has 12 pentagonal sides. Many new players mistake the d12 for the d20. This is an honest mistake, and no one should think any less of you for doing this. Even veteran players (myself included) make this mistake from time to time. If you have trouble, look at a d12 and a d20 side-by-side. A d12 has pentagonal (five-sided) faces, while a d20 has triangular (three-sided) faces.
- d20: The d20 features 20 triangular sides. Modern d20's have numbers running from 1 to 20. Older models of dice, dating back to the days when you needed to color in the numbers with a crayon, had two sets of numbers running from 1 to 10. To differentiate these numbers, you colored in the two sets in different colors. Fortunately, we don't have to do that any more.
d20's vs. "Spindown" dice
Players of Magic the Gathering may be familiar with "spindown counters". These are 20-sided dice similar to a d20, and it's easy to mix them up. However, a spindown counter is weight differently from a d20, which can skew the average rolls of the die unpredictably (think a "loaded" die).
Identifying spindown counters is simple: On a spindown counter, numbers are adjacent to each other so that you can easily count down from 20 (players start with 20 life in a typical MtG game and typically go down over time). A real d20 distributes the numbers across its surface so that the opposing sides on a d20 add up to 21.
Dice Roll Notation
Die rolls are typically listed in a notation denoting how many dice you should roll, and how many to roll: XdY+Z. X is the number of dice to roll, Y is the type of dice to roll, and Z is any static modifier to add to the die roll. 5d6 would mean to roll 5 d6's, while 2d6+2 would mean to rolled 2 d6's and add 2 to the total.
In the event that something calls you to roll multiple types of dice, the die types are typically listed in ascending die size with the flat bonuses totalled. So if you need to roll 2 six-sided dice, one 4-sided die, and add 3, you would write it as 1d4+2d6+3.
When do we roll dice?
There are a lot of opinions on this, but in general, dice are rolled when the GM and the players disagree on what happens. If the DM declares that a door is locked, but a player wants to pick the lock, the "disagreement" is settled with a dice roll. Dice are intended to create a random, impartial way of resolving conflicts and challenges in a roleplaying game, and to simulate the character attempting something which has a chance of meaningful failure.