Skills are special abilities that can be used using hotkey assigned in the controls settings. Skills can be unlocked through progression or item affixes.
Skills have levels to them that allow them to get progressively better. Skills levels can be obtained through progression or item affixes.
Class specific skills can only be used when using a weapon that matches that of the skill.
Skill specializations are ways to change or modify the skill on the base layer. Something that alters the skill drastically. Each of the large triangles is a skill specialization. Such as changing the nova from a fire, lightning, or frost nova. Only one skill specialization can be selected for a given skill.
Augmentations are itemized upgrades for skills. Augmentation orbs are in the global drop pool. Augmentation orbs can be applied to any skill to unlock an augmentation slot. These augmentation slots can now be modified to be one of the existing augmentations listed above. By default only 2 augmentations can be applied to any skill but further progression introduced through some future means may unlock the ability to have more. Skill augmentations will apply to several different skills and are intended to be more generic. Some augmentations that are created may not work for some skill specializations. Such as maybe we have some sort of increased fire damage augmentation or something, but if the skill doesn’t deal fire damage then it wouldn’t be able to be assigned.