If you open Devices window by going to Window top menu and clicking on Devices (or by pressing F7) you can insert an Art-Net node by right-clicking somewhere in the empty area and hovering above Art-Net node and clicking on Add new.
A new popup window will open where you set the IP address of the node.
Once you’ve done that and after selecting the node you can, on the right side, set Number of ports and Start universe. The number of ports tells you how many DMX outputs the node has. Usually, you can simply count the number of XLR outputs on the node. Start universe allows Lightact to know which fixture should be sent to which node. For example, let’s say you’ve got 2 eDMX fixtures: Fixture 1 and Fixture 2. Both having start channel set to 1, but Fixture 1 has start universe set to 1 and Fixture 2 to 2. And say you’ve got 1 Art-Net node with 2 universes (and hence 2 DMX outputs). If you set Start universe of the node to 1, then Fixture 1 will be sent to first DMX output and Fixture 2 to the second output. But if you set Start universe of the node to 2, then Fixture 1 won’t be sent to this node at all and Fixture 2 will be sent to first DMX output.