As you explore the island you have found yourself marooned on you need to collect resources so you can craft and make a shelter which you can use as a base and weapons so you can hunt and defend yourself.
You will soon realise that everything you find on the island is a resource of some sort which you will be able to put to good use. For example most of the trees on the island will produce wood or thatch which you can use to build your shelter and make a campfire and the rocks will give you flint which you need to light a fire.
All the resources you collect go into your inventory and a crafting table can be accessed whenever you need it by tapping the small backback icon in the upper-left corner of the screen followed by the 'Inventory' tab to the right which will default to the 'Crafting' menu.
The first thing you will be able to craft will be a stone pick which will require wood, thatch and stone.