Setup A Client
From The MegaTF/TeamFortress Wiki!
Step 1. Download and install Quake from Steam. Quake should download into your steam directory. Example: C:\Program Files (x86)\Steam\steamapps\common\Quake. If you already own quake ignore step 1.
Step 2. Download and unzip Fortress into your Quake folder.
Step 3. Download and unzip ezQuake into your Quake folder.
Step 4. Setup your Configs
Step 5. Find a server at Active Servers or quakeservers.net
Step 6. Launch "ezquake.exe" in your Quake folder to play!
Eye Candy
For a modern quake experience make sure you run the ezquake graphics on "eyecandy" mode. Also visit the Graphical Replacements page for high quality map retextures, skyboxes, audio upgrade, etc..