Copy all the files in the newly downloaded zip folder to your Titanfall2 folder. This can vary depending on whether you purchased the game off Steam or Origin, and if you set a custom folder for game installs.
For Steam - Right click Titanfall 2 > Properties > Local Files > Browse Usually: C:\Program Files (x86)\Steam\steamapps\common\Titanfall2
For Origin - To find the location of your Origin library go to Origin -> Application Settings -> Installs & Saves -> On your Computer -> Game Library Location Go to the directory mentioned there using File Explorer and open the Titanfall2 folder.
Usually: C:\Program Files (x86)\Origin Games\Titanfall2
For EA App - To find the location of your EA library go to Settings -> Download Go to the directory under "Install location" using File Explorer and open the Titanfall2 folder.
Usually: C:\Program Files\EA Games\Titanfall2
Launch NorthstarLauncher.exe to start Northstar
After launching for the first time, you'll be greeted with a popup requesting to authenticate to the master server. Click Yes (This can be changed in the mods menu later if desired)
Select Launch Northstar
From the multiplayer menu, you can use the server browser to select and join any of the public community hosted servers.
If you're having issues with running or setting up the Northstar client or are thinking of running a dedicated server you can find help and troubleshooting tips on the wiki and the Discord server: