turtle.refuel Is an command in ComputerCraft that attempts to refuel a Turtle using smeltables in its inventory. Fuel is necessary for Turtle movement and can be added manually by the player in its shell interface with the command, refuel <number>. The turtle.refuel command instructs the Turtle to do this for itself, allowing for full automization. It returns True if any fuel is added to the Turtle.
where <number> is the number of smeltables to use as fuel in the selected slot