Firemaking General

Firemaking is not one of the most useful skills in Runescape Classic. However, there are still some uses for it. It is used for making a campfire where you can cook your freshly caught fish or uncooked stews.

For lighting a fire, you will need a log.

To obtain these, you have to use your Woodcutting Skill which is detailed in the Woodcutting Guide.

To light a log you need a tinderbox.

Drop your log and then use your tinderbox on the log. Your character will then try to light the log if your firemaking is high enough. The higher your Firemaking the fewer tries you have to make.
Firemaking Guide
Only the logs of normal trees can be burnt and you can burn logs anywhere you want. To burn a log, drop it on the ground and use a tinderbox with the dropped log.

The formula for xp's per level is: Level * 1.75 + 25.

You will need to burn exactly 73,490 logs to get to 99 firemaking.