From the word itself, Magic is all about spells and the way you mange them. Imagine, you and your buddy are playing. You cast a spell, but your friend casts something too. Then you argue that you were first, but your friend says otherwise. Then you begin to slap each others face. Then there's a brawl and you could hear people shouting and cheering. Do you want that to happen? Wouldn't that be so chaotic? haha That's why Wizards created a system of taking turns and casting spells one at a time.

Hence, we came to know about the terms "Priority and Stack."  They are all weaved together as they are inter related..



PRIORITY

In the law of physics, an object can't be in two places simultaneously. And so is in magic, you too can't cast spells simultaneously, and players can't cast spells at the same time - actually, I call this common sense.  

Priority is a guideline that tells which player could make actions (spells, abilities)  at a given point of time. From the word itself, it means something that must be done first or needs more attention than anything else.
And we need this kind of system because things gradually complicates as numerous actions are made.

When you are given priority, you can:
1. cast a spell 
2. activate an ability
3. or just pass (you chose to do n0thing) and give the priority to your buddy

And so, if you don't have priority, you can't do anything yet. You can't EVEN respond to any actions made by your opponent - unless he passes it down to you.

But note, it's going to be silly if you'll say, "Hey dude, I'm passing the priority to you now." We don't do that OK? This is implicit in nature. That's why it's of great importance that we know the basics as this could be used against you by your opponents and vice versa.

So how would you know if you have the priority?

1. "Whenever you  play a spell, ability, or make an action, you are going to have the priority again - until you pass it."

    Deeper elaboration through example:
        
        1. Let's say Player A started with Priority.
            He casts FIREBALL aiming for 8 damage.
            After that, priority is again given to him.
            He can choose to play another spell again. Or he can choose to do nothing.

            Let's say, Player A doesn't want to play another spell.
            Note: This is the time to PASS the priority to Player B.

        2. Player B now receives priority from player A.
            He casts HEROES' REUNION because his life is down to 2.  
            After that he receives priority again.
            He can choose to play another spell again. Or he can choose to do nothing.

            But he casts HEALING SALVE.
            He receives priority again.
    
            He can choose to play another spell again. Or pass the priority.
            And so on and so forth.
        
2. "Whenever something (effects, spells, actions, etc)  takes effect or RESOLVES, the active player receives the priority."
     
            Before we begin any game, we agree who's gonna go first and who's gonna draw, right? If you choose to play, you are the ACTIVE PLAYER.

            As you can observe in the sample above, those spells HAVE NOT RESOLVED YET, they won't take effect yet.
            What would happen now if those spells resolves?
         
    How do spells resolve?
            This happens when both players passes priorities. In this case, Player B will pass the priority to Player A after casting
    HEROES' REUNION. Player A will receive the priority but opted not to do anything. When this happens, the spell (HEROES' reunion) will resolve.
            The first spell that we have to take out from this scenario is the very recent one. This is a process we call "F.I.L.A."  First in, Last out.
    To widen it further, prior spells would be on stand-by while we let the very recent spell resolves.
            *** VERY IMPORTANT NOTE:  SPELLS RESOLVE ONE AT A TIME. But any player may cast a spell within the intervals.

    Let's make it a little bit serious now.


     1. Player A. Priority.
            FIREBALL.
            Priority.
            Passes.
          
        2. Player B. Receives Priority
            HEROES' REUNION
            Priority
            HEALING SALVE
            Priority
   
        But before we proceed, I'd like share another commonly used term in MTG which is as important as these things because they are all connected with each other. The imaginary place where we put all the spells, abilities, and effects is what we call the "STACK." When you stack up papers, what do you do? Isn't that you put one over another? The same goes here at MTG. We systematically stack up spells, effects, and abilities one over another to avoid chaos and confusion. This also serves to help us track the actions that had happened. Note that we NEVER pull out spells in the middle of the stack. We only use FILA. The very last spell will resolve first and will always be.       
  
        In our sample here, both players passes priorities. The very first spell that resolves is HEALING SALVE since it's the most recent spell that was cast. When it resolves, Player B will have the priority again. What would happen after this is quite interesting. Because Player B can choose to cast another spell since he has priority. If he passes, player A gains priority and can cast spells in response to the HEROES' reunion.

       This is where it gets complicated at times. But don't worry because our main goal here is to give effective solution to these things.

       To help us imagine the scenario even better, we are going to apply Stack. This is how it goes:
                        HEALING SALVE 
                        HEROES' REUNION
                        FIREBALL - 8 damage

        HEALING SALVE resolves, Player B gains 3 lives more making his life total at 5. Player B has nothing to do and passes the priority. Spells left on the stack are:
                        HEROES' REUNION 
                        FIREBALL - 8 damage
   
     Player A receives Priority. He has 2 Searing spears at his hand. He casts one SEARING SPEAR and is put on the stack. This is how it looks:
                        SEARING SPEAR
                        HEROES' REUNION 
                        FIREBALL - 8 damage


     Player A receives priority again. Then he opted to play the 2nd SEARING SPEAR. He passes the priority.
                        2nd SEARING SPEAR
                        1st SEARING SPEAR
                        HEROES'  REUNION 
                        FIREBALL - 8 damage
   
    Player B receives priority. But he has no spell to cast! So he passes as well.

    The 2nd SEARING SPEAR resolves. It deals 3 damage to player B. He's down at 2 lives.
                        1st SEARING SPEAR
                        HEROES' REUNION 
                        FIREBALL - 8 damage

    Player A receives priority after it resolved because he is the ACTIVE PLAYER. He passes.
    Player B receives priority. But he passes as again.
  
    So, the 1st SEARING SPEAR resolves. Player B loses.
  
    Is this somehow relevant to you? Have you had this scenario before? This is just a common scenario. There are still other ones which are more complicated. The only way you could be well versed on these things is to play a lot and apply all that we've just talked about.

One more thing before we end this lesson. When we play land, we receive priority immediately afterwards. Ok?
When we put a planes walker into play, we receive priority. That's why we can use it's ability right away, right?

I am curious as to how helpful this article was - I really hope so. If you found it useful (or if you found it useless), please let me know as I'm very open to all feedback and suggestions.

I am considering writing more articles related to this one such as how you could possibly make use of these things to your advantage, etc., etc., etc.

I hope this somewhat had helped you one way or another. Let me know Please. Thanks for reading! Happy playing!