In the case of an MMORPG, networking is about connecting people. This tutorial will teach you the theoretical aspects of networking your players, the foundation of an MMORPG's infrastructure!
If networking is the infrastructure, then the server is the core. A server is a central computer running a server program. The server manages every aspect of the game and relays relevant information to clients.
A client, or user, run their client program to start the game and connect to the server. They retrieve their character information from the server, and any important actions from the server are executed on the client.
Clients rarely connect to each other (and for a variety of reasons, shouldn't). If a client sends a chat message, for example, it goes from the client, to the server, to the other clients.
To establish a proper MMORPG, you need to network each player to the server, and then to the other players. If your players aren't networked, you don't have an MMORPG.
Game Maker itself contains some functionality to network players, however the built-in functions (known as Mplay) are not very powerful or user friendly, and are under commonly criticized as one of Game Maker most flawed inclusions.
To achieve powerful networking functionality, we use an application extension known as the 39dll.
Using this DLL, you can begin to setup a network between the clients and the server. While this task is moderately complex, the Networking ApplicationTutorial will take you step-by-step through the process of setting up your network. But first, it's important that you learn about networking as a concept. This will help you understand the application side of development much quicker.