You will need a sawmill if you want to create planks. A lot of recipes use planks so this item is necessary to have on your Island.
How A Sawmill Is Made
First, you will need to go to your workbench and open it by pressing “F”. Click on the Utility button to the left. Hover your cursor over the items until you see “SAWMILL”. Click on it.
The recipe for the sawmill is 10 WOOD and 10 IRON INGOT. Place your sawmill once it is crafted. To open it, press “F”. You will need a source of fuel to run it, like coal. Once you open it, you will see all the items in your inventory that you can use with it.