RedNet PCIe/PCIeR cards must be installed in PCIe slots or a Thunderbolt-PCIe chassis connected to the computer (see this article for a list of supported chassis).
Once the card is installed, ensure that the driver for the PCIe/PCIeR card is also installed. The driver is bundled with RedNet Control and there's an option midway through the installer to install the PCIe driver:
Connecting to the network
Once the card is connected to your computer and the driver's installed you will be able to select it as the input/output in your DAW. In order to route between the RedNet PCIe/PCIeR card and other Dante devices the PCIe/PCIeR card must be connected to the Dante network over ethernet (cat 5e or better).
The RedNet PCIe/PCIeR card is not a 'regular' ethernet port (NIC). This being the case, in order to view what devices are available on the Dante network from the computer, you must also connect a 'regular' ethernet port on the computer to the Dante network. No audio is passing over this connection and it's just used so that you can view the current state of the Dante network and setup routing between devices. Once your routing is set up you can safely disconnect the cable from the computer to the network and audio will still pass between your RedNet PCIe/PCIeR card and other Dante devices.
A simple diagram showing a PCIe card in a Thunderbolt-PCIe chassis connected to a Mac Pro is shown below: