The first item you should consider crafting is the fishing rod. You will be able to craft one from two pieces of string and three pieces of wood so make sure you keep an eye out for these materials as you begin to explore the island. Once you have crafted a fishing rod you will be able to use it to help you catch fish and prevent potentially fatal hunger.
To actually use the fishing rod you need to go to a body of water and keep on going until the fish symbol appears on your screen instead of the hand with a sword. Tap the fish symbol once and when the string goes to the side tap it again. If you now look in your inventory you will notice that a fish has appeared.