There are a number of collectibles to gather in Kao the Kangaroo, with Scrolls being one of them. Scrolls will give you some lore to read about the game’s world, such as the characters and enemies you come across. This page will detail the Scroll you find in The Lava Caves.
After collecting the third Rune, you will find a lone Range Frogster on a platform just a little ahead. Defeat the Frogster by either reflecting its projectile back at it or just hopping on its platform and smacking it. There will be some other platforms to jump to this in this area, which leads to a large spider web. That means you will need a fire orb charge, of which there are plenty throughout the level, especially if you make use of the Fire Totems that spit them out infinitely. Burn the web with any attack while charged, revealing the Scroll behind it.