Shall we play a game?
To play together the players first need to find and join the same game. The peer that setup the game is called the host and the other are then clients. In the end it is common that the host also turn out to be the server of the game but it is not always so.
Direct Connect - 1993
With a direct connect system the player can enter the IP or DNS of a host directly to join it.
Server Browser - 1996
The game query a Master server of all the existing host and list them for the player. Pick one to play on and press connect to join it. For a LAN game it can simply query the local network for any servers.
Contact List - 1996
List your friends and give you a quick way to join or invite them if they are online.
Playlists - 2004
With this system the player select a type of game to play. The master server then connects the players with the same preferences and pick one of them as host and the game start. The player do not have to spend the time with settings or looking for a server as it simply works when he selects his preferred play style.
Ranking - 2004
A ranking system works like a playlists system but it also try to match the player so people that are around the same skill level face each other. This is done by updating a rating value for the player as he wins or loose games.
TrueSkill™ Ranking System - 2015