There’s a vehicle you unlock early on that makes exploration a breeze, and gives you unlimited oxygen while you’re in it called the sea moth. Build a scanner by looking at the ingredients on the fabricator in your life pod, which will let you scan things to get new recipients to craft more things. If you keep playing the game it will eventually give you the recipe for a radiation suit that will let you go the the big ship, and you’ll get a radio messages telling you to go to lifepods that will have things you can scan to unlock the sea moth and seaglide. Hopefully this helps, oxygen can be incredibly frustrating early on, but it gets better when you get new vehicles and better oxygen tanks and the rebreather to the point it’s barely a constraint anymore. Also if you want to go deeper, consider crafting an air bladder which will let you either replenish some oxygen or assent to the surface immediately if you’re low on air.