user18625: When I started playing chess, I learned many of the rules of chess on my own.
I was playing chess online, and then I realised that pawns can capture in such a fashion. At first, it was weird to me. Like, wow! How can a pawn capture like this?!
Then I read the theory of en passant. I have come to know that such kinds of rules exist in chess. By the way, it's an interesting rule.
Now here comes the main question: How can we teach this rule to a beginner (in a plain language or simplified way or associating any story to it)?

user15078: In simple words: if a pawn jumps two squares and lands right next to an opponent's pawn, then the opponent can capture that pawn in the following turn as if it had moved only 1 square. That is, only right after you made your jump, your opponent has the option to take by en passant, past that turn it is no longer allowed.
So keywords to remember: two square move, right next to, and following turn. 
Visually:
 [title "Visualised example"]
 [fen "r1bqkbnr/pppppppp/2n5/4P3/8/8/PPPP1PPP/RNBQKBNR b KQkq - 0 2"]

 1...d5 2.exd6 (1...d6 2.exd6)

Notice the end scenarios are the same after either d6 and d5, as in after the capture one cannot tell if it had been by en passant or a normal capture.
Intuitively, you can imagine the rule is there so that one cannot jump past another pawn and completely evade the option of a trade. Exactly similar to when you move your pawn only one square, and your opponent still has the option to capture your pawn if they so desire. 

user4418: 
How can we teach this rule to a Beginner? (in a plain language or
  simplified way or associating any story to it)

The history gives the story.
At one time pawns could only move one square at a time even on the first move. But this made the game a bit slow. To speed it up the rule was changed to allow a pawn to move either one square, as before, or two squares on the first move. 
But this changed the way one pawn could stop another pawn from moving because of the risk of capture. So, for instance, a black pawn on g4 stops a white pawn on h2 from moving. Before the rule change the only move the white pawn could make was from h2 to h3. Then the black pawn on g4 could capture it. After the rule change the black pawn could move straight from h2 to h4 thereby dodging the attack from the black pawn. This was unfair to the black pawn on g4 and changed the game in an unintended way. So, to even things up again the en passant rule was introduced which said that in that situation the g4 black pawn could take the h4 white pawn as if it had only moved one square. 
The rule only applies on the move immediately after the double pawn move because with the old rule (only allowed to move one square on move one) if black didn't take immediately then white could move the pawn on his next move and the chance was gone.

18625: <p>When I started playing chess, I learned many of the rules of chess on my own.
I was playing chess online, and then I realised that pawns can capture in such a fashion. At first, it was weird to me. Like, wow! How can a pawn capture like this?!</p>

<p>Then I read the theory of en passant. I have come to know that such kinds of rules exist in chess. By the way, it's an interesting rule.</p>

<p>Now here comes the main question: How can we teach this rule to a beginner (in a plain language or simplified way or associating any story to it)?</p>
 15078: <p>In simple words: if a pawn jumps <strong>two</strong> squares and lands <strong>right next</strong> to an opponent's pawn, then the opponent can capture that pawn in the <strong>following turn</strong> as if it had moved only 1 square. That is, only right after you made your jump, your opponent has the option to take by en passant, past that turn it is no longer allowed.</p>

<p>So keywords to remember: <strong>two square move, right next to, and following turn</strong>. </p>

<p>Visually:</p>

<pre><code> [title "Visualised example"]
 [fen "r1bqkbnr/pppppppp/2n5/4P3/8/8/PPPP1PPP/RNBQKBNR b KQkq - 0 2"]

 1...d5 2.exd6 (1...d6 2.exd6)
</code></pre>

<p>Notice the end scenarios are the same after either <code>d6</code> and <code>d5</code>, as in after the capture one cannot tell if it had been by en passant or a normal capture.</p>

<p>Intuitively, you can imagine the rule is there so that one cannot jump past another pawn and <strong>completely evade</strong> the option of a trade. Exactly similar to when you move your pawn only one square, and your opponent still has the option to capture your pawn if they so desire. </p>
 4418: <blockquote>
  <p>How can we teach this rule to a Beginner? (in a plain language or
  simplified way or associating any story to it)</p>
</blockquote>

<p>The history gives the story.</p>

<p>At one time pawns could only move one square at a time even on the first move. But this made the game a bit slow. To speed it up the rule was changed to allow a pawn to move either one square, as before, or two squares on the first move. </p>

<p>But this changed the way one pawn could stop another pawn from moving because of the risk of capture. So, for instance, a black pawn on g4 stops a white pawn on h2 from moving. Before the rule change the only move the white pawn could make was from h2 to h3. Then the black pawn on g4 could capture it. After the rule change the black pawn could move straight from h2 to h4 thereby dodging the attack from the black pawn. This was unfair to the black pawn on g4 and changed the game in an unintended way. So, to even things up again the en passant rule was introduced which said that in that situation the g4 black pawn could take the h4 white pawn as if it had only moved one square. </p>

<p>The rule only applies on the move immediately after the double pawn move because with the old rule (only allowed to move one square on move one) if black didn't take immediately then white could move the pawn on his next move and the chance was gone.</p>
