How to make fires? To make a fire, players need any log and a Tinderbox. Use the Tinderbox on the Log.
After you have created a succesfull fire you can Right click the fire and click "Use" to throw some more logs on that.
How to buy Tinderbox? Players can buy this at the Grand Exchange adding a +5% on the buy option.
What to burn at what level?
Level 1 - Logs Level 15 - Oak Logs Level 30 - Willow Logs Level 35 - Teak Logs Level 45 - Maple Logs Level 50 - Mahogany Logs Level 60 - Yew Logs Level 75 - Magic Logs