If you have access to a WiFi network, then you can configure the D4 and the WT-5 to connect to the existing network's access point. This is "infrastructure mode" and the most common way people use WiFi in their homes, businesses and offices.
If you don't have an existing WiFi network, the you can directly couple the D4 to the WT-5. This is "ad hoc" mode, where the two devices talk directly to each other instead of using an existing WiFi network.
So if you are indoors and wish to use your church's network, follow the instructions to set up for infrastructure mode. If you are outdoors and can't connect to the existing network, use ad hoc mode.
Or you can use ad hoc mode in both places and not have to reconfigure when you go from indoors to outdoors.