What are the online features of this game?

In order to access online features, you will need to build a Radio Tower in order to establish communication. The Radio Tower will enable the chat function, and you'll be able to make friends, join parties, or become a part of a clan. Here are the materials that you will need:

10 Pine Plank, 5 Wiring, 5 Iron Bar, 3 Transistor

You also need to be level 28 in order to craft this item. Later on you'll be able to participate in Ambushes as well.