You connect the air hose to the one on the left, yes (with the black screw on the top). The second air intake (middle) is for an ozone system. Note that there are three adjustments for the Nyos:
1. The black screw (controls the amount of air let into the skimmer).
2. The actual pipe connected to the open/close valve, which is used to set the initial water level.
3. The open/close valve for fine-tuning the water level.
Start out with the black screw closed (no air), the open/close valve closed all the way and then turn the pipe to set the initial water level (about 4" below where the collection container attaches). Open the black air valve so there's maybe a 1/16" gap and then fine-tune the water level with the open/close valve such that the foam is just below where the collection container is. As a new skimmer it will tend to foam a lot for the first few days until it breaks in.
