A macro uses a chain of skills while you hold one key. Players use it in these cases:
Cancel animations for more damage. Hold left click and the macro key together. A black shadow behind your character shows each cancel.
Two rows of skills over the same time. Without cancel, every skill plays its whole animation. With cancel, a left click cuts the end of each animation, a black shadow shows it, and the next skill starts sooner. So more skills fit in the same time.
Start a boss fight. Press your buffs by hand first, then hold the macro key and left click.
Farm mobs with one key. Add basic attack as a macro step and hold only the macro key. You lose a little damage.
Run out of skill bar keys. Put two skill bar slots in one macro. One held key then runs both.
Skills that need another skill first. Put both in the macro. It skips the second skill until the first one sets it up.
Keep buffs and long cooldown skills out, or the macro spends them on weak mobs. Keep toggles, charge skills, dodges and rushes on their own keys. The macro turns a toggle off and fires a charge skill uncharged.
Open the skill window and click the macro button at the top right. Add a step for each skill bar key it should press. Bind the macro to a key in Key Settings, General, under Gameplay. Hold that key to run it. You get 3 skill presets, and each keeps its own macro.
Usually it has no key yet. The macro key is empty at first, so the macro does nothing until you bind one in Key Settings.
The macro runs only while you hold its key, so many players put it on right click, next to the basic attack. Quick Use 2 also sits on T by default. Some players use Z.
Why does my macro only use one skill?
Hold the macro key down. The macro only runs while you hold it. If it still uses one skill, check the skills stacked on that key. The bottom skill goes first whenever it is ready. A skill with no cooldown there is always ready, so the skills above it never come up. Put it at the top instead.
Does the macro wait for a skill that is on cooldown?
No. It skips any skill on cooldown and goes on to the next step it can use. It doesn't stop to wait for it.
What does the delay between macro steps do?
It is the pause between one step and the next, in ms. Each step starts at 10 ms, the lowest you can set, and you can raise it up to 9,900 ms. It is a pause inside the macro, not the lag between you and the server.
Can an outside macro program get me banned?
Yes, it can. The rules punish unauthorized programs and devices with an account ban. Accounts have been restricted for macros, bots and other unauthorized programs.
In Korea, NC once blocked the game while Logitech G HUB, Razer Synapse or Corsair iCUE ran. It still checks for macro use. The game's own macro is allowed.
Gladiator Load Main line For most of your damage against monsters. 
Rage Burst
Overhead Slam
Rending Blow
Templar Load Shield Smite line Shield Smite makes Judgment usable for a moment, so Judgment comes right after it. 
Shield Smite
Judgment
Assassin Load Damage line For steady damage on one target. The skill with the longest cooldown goes first. 
Insignia Explosion
Heart Gore
Savage Roar
Ranger Load Griffon and Gale lines For steady damage. The Griffon line goes first, then the Gale line. 
Griffon Arrow
Snare Shot
Burst Arrow
Gale Arrow
Drill Dart
Tempest Shot
Spiritmaster Load Spirits and Elemental Fusion Summons your spirits and spends Four Elements on Elemental Fusion. Fire Spirit goes last, so it stays out the longest. 
Elemental Fusion
Summon: Water Spirit
Summon: Earth Spirit
Summon: Fire Spirit
Cleric Load Chain of Torment into Condemnation Condemnation works only on a target with Chain of Torment, so the buff and debuffs go first. 
Prayer of Amplification
Earth Punishment
Chain of Torment
Condemnation
Chanter Load Dark Crush line Dark Crush works only for a moment after certain skills, so it comes right after each one. 
Spinning Strike
Dark Crush
Marchutan's Wrath
Impactful Crush