Here's how to connect to your Left 4 Dead 2 server and adjust the most important settings.

Connecting

Open the server page in the client area and click Start.
Wait until the status shows “running”. You can follow the progress in the Console tab.
Copy the address (IP:Port) at the top of the server page.
In Left 4 Dead 2, enable the developer console under Options → Keyboard/Mouse, open it and enter connect IP:Port.

Important settings

In the Startup variables tab:

Default Map (SRCDS_MAP) – the map on start, e.g. c1m1_hotel (Dead Center).
Auto Update (AUTO_UPDATE) – updates the server on every restart.

Set the server name, passwords and game rules in the file left4dead2/cfg/server.cfg in the Files tab (create the file if it is missing), for example:

hostname "My server" – name of the server
sv_password "…" – password for joining
rcon_password "…" – password for admin commands via RCON

Changes take effect on the next restart.

Game mode and difficulty

These entries in left4dead2/cfg/server.cfg determine how the game is played:

sv_gametypes "coop,versus,survival,realism,scavenge" – allowed game modes
mp_gamemode coop – mode on start, for example coop or versus
z_difficulty normal – difficulty: easy, normal, hard or impossible

Joining without a lobby

So that your group lands directly on your server, add sv_allow_lobby_connect_only 0 to server.cfg. Players then join via the developer console with connect IP:port.

With sv_steamgroup and the ID of your Steam group, the lobby search prefers your server for group members.

Changing maps

Set the starting map via Default map. The campaigns start with c1m1_hotel (Dead Center), c2m1_highway (Dark Carnival), c5m1_waterfront (The Parish) and other cXm1_… maps.

Good to know

After a game update from Valve, the server must be updated too, otherwise players cannot join. With Auto Update, a restart is enough.
Upload add-ons such as SourceMod via SFTP into the left4dead2 folder.
The first start takes longer because the server files are downloaded and set up.

Left 4 Dead 2: connect to and set up your server