Armour pieces and weapons can have rune sockets for stat runes
Runes provide powerful stats like elemental resistance or maximum life
Skills come from Uncut Skill Gems; supports link into a skill's support sockets
Use Jeweller's Orbs to add support sockets to a skill (max 5: Lesser=3, Greater=4, Perfect=5)
Support gems carry tiers gated by your Uncut Support Gem level (1-3); the one-copy-per-character limit was removed in 0.3.0
Salvage quality/socketed gear at the salvage bench for crafting shards