When you spawn you are spawned on a small section of wood. For now, stay on there, and don't go for a swim, for two reasons. The first, your raft will float away, and you'll spend time chasing after it.
The second, and more obvious, is the large shark circling your raft. You can ignore him for a little while, however if you do not hurry he will start eating your raft. For now, just collect the floating resources with E.