Subnautica

• You just right-click on something to drop it while you're not in the Lifepod, and while in the Lifepod there's a storage locker.
• Catch Bladderfish for water, go to the Lifepod, use the fabricator, and it can use the fish to make water.
• Get some titanium and creepvine seeds to make a knife (make silicone rubber and then make a knife), use that on the coral tubes and find salt, it's typically near the Acid Shrooms but can be found elsewhere. Mix the salt and the coral samples to make bleach, use that to make more filtered water.
• From here I'd say just check the recipes in the Fabricator, right away you should've made a repair tool to fix the Lifepod up, it's recipe is under Personal->Tools. You'll often have to make materials to make things, so check ingredients for what you want to make, then check the Resources tabs to see if the ingredients are things you can just make.
• I'd recommend making some Fins, a few air tanks, scanner, flashlight, laser cutter, and builder tool, pretty much in that order. You'll use the scanner to scan parts and things you find on the ocean floor to get blueprints to build more stuff.
• You can also build a radiation suit, but I found one in one of the earlier Lifepods I got a signal about (I think 6 or 7), not sure if those are in an order or random, but they'll pop up in the communications module in the Lifepod.
• The First Aid module in the Lifepod will make first aid kits periodically and will beep when ready. I personally tend to keep two on me just in case and store the rest in a locker.
• You can build a battery recharger, I dumped a bunch of batteries not knowing this, you'll need the Builder Tool and maybe scanned blueprints for it
• At some point you'll get blueprints that let you make various vehicles, and once you get one you should explore a bit farther out, just remember to bring extra batteries, water, and food.
• Cooked food will eventually spoil and be bad to eat, uncooked fish won't afaik. I usually cook enough fish to fill up at the pod, then cook one for the road.