My son has already started writing a story using the vocab words

Legendary gaped glared muttered flinched fluke snickering stunned.
He is king of confused , can you correct the mistakes and help us in completing it.
Below is the story:

In December 2015 I will be playing football as a goal keeper with a legendary team"Barcelona" against "Chelsea" which both teams have strong players.
Chelsea team was stunned , how will they accept a beginner goal keeper to join their team.
The match has startred and I was ready to catch the ball. All the crowds were snickering that I will let the team loose and not get the champion. As the ball came towards me with the strongest football player"Eden Hazard" i muttered" I'm going to surprise you all".
As the ball came closer, Eden shot the ball which was not near to me but I was was able to catch it.
Every one was shocked and Eden gapped this is impossible.

I'll correct your errors. As a story, your son is doing very well!

I was going to play football as a goal keeper with a legendary team, Barcelona, against Chelsea. Both teams have strong players. The Chelsea team was stunned. How would they accept a beginner goal keeper on their team?

When the match started I was ready to catch the ball. The crowd was snickering. The were afraid I would let the team lose and not get the championship. As the strongest player, Eden Hazard, came towards me with the ball, I muttered, "I'm going to surprise you all." Eden shot the ball, which was not near to me, but I was able to catch it! Everyone was shocked. Eden gaped. This was impossible.

Note that verb tenses should match. Mixing future with past is confusing. I have inserted commas and corrected quotation marks. Barcelona and Chelsea are cities (the teams have names, which might be in quotation marks, but not the cities). I also corrected a couple of run-on sentences.

You can go on: ...this was impossible. It was a fluke. Eden Hazard glared at me. To use the word "flinched", you might write, "I flinched, but I was able to catch it."

Thank you very much...

How can I let him end the story?

Did they win the game and the championship? Win or lose, that's the end of the story.

Yes they won

Here is the corrected and completed version of the story:

In December 2015, I will be playing football as a goalkeeper with the legendary team "Barcelona" against "Chelsea," both of which have strong players.

The Chelsea team was stunned. How could they accept a beginner goalkeeper to join their team?

The match started, and I was ready to catch the ball. The crowd was snickering, thinking I would let the team down and not win the championship. As the ball came towards me, with the strongest football player, "Eden Hazard," I muttered, "I'm going to surprise you all."

As the ball came closer, Eden shot the ball, but it wasn't near me. However, I was able to catch it flawlessly.

Everyone was shocked, and Eden glared at me. He couldn't believe what just happened.