Right-click on your Oiling Trough to open it and place up to 8 Planed Boards inside.
In about 2 days the Planed Boards will become either Oiled Boards or Warped Boards at about a 50/50 chance. Each Board will consume 2x Liters of Vegetable Oil. Warped Boards can be re-planed back into Planed Boards to try again.