As a D&D player, it pays to be aware of the action economy, the same way you pay attention to your Techniques, the initiative order, and your hit points. It’s just one more thing to track to help you gain a tactical advantage and prevent disaster.
When it’s time to take an action on their turn, a character usually has big decisions to make.
In short, understanding action economy is the key to making sure that every turn you’re taking as many useful actions as possible and, perhaps even more importantly, minimizing the actions your enemies can take.
Everything on this list is considered an "Action"
Action
Your action is the thing you do to change the world around you every turn. Sometimes, that just means swinging a sword or throwing a fire bolt using the attack action, but in a situation where the action economy is stacked against you, it sometimes pays to get creative.
Finding ways to interact with your environment, like spilling burning oil across the floor to prevent your enemies from closing to melee range, or destroying a bridge to delay reinforcements can do a lot to swing the action economy in the party’s favor. If your character is a spellcaster, there are a ton of options for altering the action economy, either by increasing the number of things the party can do (like Haste for example), or by hampering your opponents.
In short, you should be thinking of your enemies’ actions almost as a secondary pool of hit points. Removing an enemy’s ability to act (more specifically to hurt you or advance its evil plans) is basically akin to giving your side a net boost to their effectiveness.
Bonus Action
Bonus actions set powerful characters and NPCs apart from the majority of monsters. Because you can only take a bonus action if you have an ability—like certain spells, bardic inspiration, hiding as a rogue, etc— that lets you do so, always ensuring you use your bonus action effectively can really empower your character, even when outnumbered.
You can only make one bonus action per turn, so make sure you choose wisely if you have multiple options.
Reaction
Reactions are even more situational than Bonus Actions, taking place only when triggered outside of your own turn by a specific set of conditions.
The most common uses for your reaction will be readying an action to occur when the time is right, and an attack of opportunity when an enemy moves out of melee range of your character without using the Disengage action.
Free Actions (and Interactions)
Free actions aren't usually something your able to do in regular D&D but in our system we have many special items and Interactions listed as free actions to keep this in line with the action economy we have limited these to 3 Per Turn.
A Free action could be as simple as dropping a weapon, Using an item you have prepared or Could be as complicated as using an entire feature. you must always be aware of what you want to in while in initiative.