Just google it. This is what came up immediately.
When you purchase a Master Weapon that you can add an augment stone to you will see a circle or two on the weapon when you are purchasing them. It will be to the far right of the name of the weapon and it will be a small gold ringed green circle. Also under page 2 of the weapon description you will see the Damage, Type, Speed and then Augments. If it says Empty then there is one...if it says Empty, Empty...then there are two. To apply the augment stone...then you would need to select it under the items menu and then it will give you a choice of Ranged, Melee, or Accessories. If you have a weapon or accessory that has an augment slot...then you can select that item and apply the augment.