To punch a tree, simply press and hold the left mouse button (PC), press the Left Bumper button (Xbox) while facing the trunk, or simply tap the trunk with your finger (PE). If you already have a Crafting Table, you can go ahead to the section on making paper.
If you’ve got more wood, feel free to convert it all to planks, but for now, all you’ll be needing are 4 Wood Planks