Forgotten Realms is one of the most popular of the campaign settings published by Wizards of the Coast (and formerly TSR) Many of the most popular characters and places in D&D books and published works reside in the forgotten realms. Many of the computer games that wizards has published have come out under the forgotten realms label. Baldurs gate 1 &2, Icewind Dale, and neverwinter nights are all games published in the forgotten realms setting.
The focus of the Forgotten Realms setting is the continent of Faerûn, part of the fictional world of Toril, an Earth-like planet with many similarities to the real world.The lands of the Forgotten Realms are shared by humans, dwarves, elves, goblins, orcs, and other peoples and creatures. Technologically, the world of the Forgotten Realms is not very advanced; in this respect, it resembles the pre-industrial Earth of the 13th century. The presence of magic provides an additional element that does not exist in the real world. There are various nation states and many independent cities, with loose alliances being formed for defense or conquest. Trade is performed by ship or horse-drawn vehicle, and manufacturing is based loosely upon cottage industry.
Religion plays a large role in the Forgotten Realms, with deities and their followers being an integral part of the world. They do not have a passive role, but answer prayers, influence mortal affairs, and have their own personal agendas. A huge number of diverse deities exist within several polytheistic pantheons; a large number of published supplements have documented many of them.
Much of the history of The Realms detailed in novels and source books concerns the actions of various deities and The Chosen (mortal representatives with a portion of their deities' power) such as Elminster, Fzoul Chembryl, Midnight (who later became the new embodiment of the goddess of magic, Mystra), and the Seven Sisters.
As a new D&D player Forgotten Realms can be a great place to start a campaign, over the last 40 years wizards, and TSR has detailed many of the regions and there are many books and games to supplement a new players knowledge of the realms.