Answer:
They let you find the runecrafting altar. You also need either a talisman or a tiara to enter the altar, once you find it. Once you know the location of the altar, a tiara is better than a talisman: you can wear it on your head, which saves one space in your inventory. Note: To craft air runes, you need to find the Air Altar (location south of Falador; see the RuneScape manual for locations of other altars). You also need an air talisman, or an air tiara. Don't forget to take some rune essence with you - this is what you will convert to air runes. Once you have the required level, better switch to crafting other runes, since they give you more experience.