The bottom line is that Dungeons and Dragons have been around for some time, and have entertained millions of people around the world due to their open world, open fantasy based games.
Dungeons and Dragons have expanded into a multi-billion dollar idea that has given rise to multiple copies of the D20 system. The game quickly grew in popularity and the demand for the original book Skyline Rocket.
D&D is a D20 system. D20 systems are role-playing games where each player has a character sheet with statistics, equipment, spells, races, ages, classes, and other abilities.
It is called a D20 system because most actions require the player to roll a 20 sided die. D stands for die, 20 the number of sides on the die. In D&D the D20 is used to attack, make saving throws to avoid spell damage, or to use an ability such as stealth or intimidation.
Damage rolls on successful attack rolls usually use D6, D8, D10, or D12s. The main focus players have in their characters are the abilities and attacks they can perform. Abilities and attacks depend greatly upon the class of the character.
Dungeons and Dragons have a plethora of classes for players to choose from. They can choose from a basic fighter, barbarian, magician, sorcerer, bard, maulvi, monk, Rajput to a druid. There are over 40 different classes for players to choose from, even more prestige (extension) classes. Each class has different abilities and plays a different role in the party.