Class compliant devices are some of the most user friendly devices for computers- often it just comes down to plug and play. Sometimes however it's possible to plug in your device, open up your DAW and suddenly find there's no input. Why is this happening?
The answer lies in your Audio Midi Setup utility. If you do not know where that is, use your Mac's spotlight search in the top right and search Audio Midi Setup.
Inside here you may find that there are two USB Audio Codec devices; one that has 2 inputs and no outputs, another with no inputs and 2 outputs.
This is a sign that your computer has split the interface into two separate devices, which need to be combined into one because most DAWs will not let you use 2 different audio devices at once.
To accomplish this, you're going to want to click the bottom left + symbol and click Create Aggregate Device from this new submenu.
This will create an aggregate device, which you can then select which sources are included in it by checking off the Use boxes next to the devices, and rename it to whatever you wish by clicking on the name in the left hand column.
This will be the device that you use inside your DAW moving forward and giving you full access to the Audio Interface.