“Why do I keep suffocating?” Well, if you wander too far from your pod, then you’ll see the little blue tether that is feeding your character oxygen disappear. You’ll be fine for a minute or so, but as you’re exploring, you’ll notice your oxygen will steadily deplete. In order to refill your oxygen meter, walk back towards to your pod until the blue line appears again.
If you find the Compound resource, stock up on it, and use it to build tethers. You can do this by accessing your backpack by pressing Q and then crafting it there. Once you’ve built tethers, you can begin placing them down by pressing T. Do this as you’re walking further away from your pod. This will allow you to keep a steady flow of oxygen and prevent your character from suffocating.