[2021] How to install Livonia DLC on Steam?

You install DLC in Steam by going to DayZ in your Steam Library, and either in the Properties->DLC or on the right-hand side you will find a box labelled DLC where you can manage your DLC (including checking boxes to install/uninstall).

The "DayZ Experimental" app is our experimental branch where we test updates publicly before they hit the main game.