The concepts that decide a Support game, what players of the role actually do at every rank, and what the role's communities advise.
How it works
How the game behaves, in plain words.
Vision
Wards show you where enemies are; a control ward also reveals and disables enemy wards near it. Ward the river or the enemy jungle entrance before you push forward, and place a control ward where you will fight later. Your trinket recharges, so use it whenever it is ready.
In bot lane the two of you trade together: the lane goes to the pair whose damage and crowd control land first. Step forward together and back off together, and back at the same time when you can, so neither of you is left alone two-against-one.
When to leave the lane
When your bot laner backs, you are free for a moment: place wards for your team, or help mid or your jungler, and be back before your bot laner returns to lane.
In a fight a support either starts it (engage) or protects the carries (peel): stand between the enemy divers and your damage dealers, and use your crowd control on whoever reaches them.
Minion aggro
If you hit an enemy champion with an attack or a spell while you are near their minions, those minions switch to attacking you for a few seconds. Trading next to a bigger enemy wave costs you extra health, so trade when the enemy wave is small or your own wave is bigger. Enemy towers do the same: hitting a champion under their tower makes the tower target you.
Objectives
Dragons, Void Grubs, the Rift Herald and Baron give your whole team gold or power. Push your wave, back and buy before they spawn so you arrive first with full health. A team that arrives late, with waves crashing into its towers, loses the objective and the plates.
Back when it costs the least: right after your wave crashes into their tower, when you have the gold for an item or component that changes a fight, or before an objective your team is going to contest. Backing with a big wave about to hit your tower loses minions and tower plates.