how to use stones

Please tell me how to make use of those stones

They're used for upgrading your pet and more importantly your weapons. Specific stones will increase the level cap on your weapons, with Power Stones being able to ascend their Tier. The pet dragon needs whatever 10 stones asked for to level up each time.

Thats true. But after 10 levels it is costly. You will be needing those stones on your weapons to upgrade. Specially on those 4 unique sets.