The client of Neverwinter Nights is the part of the game that most players see, and it is in fact considered "the game" by many players. The other part of the game is the server, and the distinction between client and server is usually only important in a multiplayer environment — the client is what runs on each player's computer, while the server is what runs on the host computer. The client provides the player's graphical user interface, while the server loads the module being played.

There are two modes in which the game client can operate. The more common mode is started by clicking "Play" from the opening (splash) menu or by running nwmain.exe directly. The less common mode is the DM client, which is started by clicking "DM Client" from the opening menu or by running nwmain.exe with the command line parameter -dmc. The DM client is intended for Dungeon Masters and is restricted to multiplayer games. Furthermore, most servers require a password for anyone attempting to connect as a Dungeon Master (i.e. with the DM client).

Connecting a client to a server is handled automatically and invisibly in single-player mode. For multiplayer games, a server needs to be selected from a list. This list is obtained by going to the "Multiplayer" section and clicking either "Join Internet Game" (for games hosted over the internet) or "Join LAN Game" (for games hosted locally, such as over a home network). During this process, the player will be asked for a user name and password. For internet games, these are authenticated by BioWare's master server, but for LAN games, if there is no internet connection then these can be anything, provided each player chooses a different name. User names are case-sensitive and are used by the server to prevent one player from taking over the characters of another.

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