1.) You did not spell "graMMatical" correctly. I'll check for others now.
2.) There are several errors. I will rewrite and add an edit in a moment.
3.) Your errors are minor, so you will have to look closely to compare my rewrite with your original. If Yahoo allowed me to post in a different color, I would make the changes in a different color so you could see them easily.
In the olden days the people of Parsimville were conceited, arrogant, and above all terrible people. They pushed their afflictions onto others, like making me, the Minor Cannon, do all of the toilsome tasks.
It was a cold and unloving time. Everyone cared only about themselves, and did not want to lend a hand to anyone. But everything changed when the glorious Griffon came.
The Griffon was a wise and astounding creature. There was an air around him that demanded and always received respect. Every day he would visit the church to see the statue of his likeness. This is how we met. The townspeople were so afraid of the Griffon that the second they saw him they made me responsible for keeping him joyful.
Slowly the Griffon began to have a good impact on the townspeople. (THE NEXT SENTENCE HAS A BIG PROBLEM. YOU SHOULD NOT SAY "AS WELL AS GOLD", SINCE GOLD IS "GOOD". NOUNS ARE GOOD, BUT VERBS CAN BE WELL. CHANGE "BEHAVED" TO A NOUN. THAT NOUN IS "BEHAVIOR", WHICH THEN ALLOWS YOU TO SAY "GOOD AS GOLD", WHICH SOUNDS BETTER.)
The behavior of the “bad” children that I taught became as good as gold, and the townspeople began to work and do things for themselves. Things were changing for the better.
After the Griffon left Parsimville, the townspeople continued their newly adapted ways of life, going to church, taking care of their own problems, and helping others. Eventually they forgot that the only reason they had changed was because they feared the Griffon, and their ways became something all people were expected to do. The Griffon changed Parsimville from a despicable place to a marvelous town of unison. For that I am grateful.
I wrote my comments in all capital letters to make sure you know that is only my comment, and not part of what you should write. If anything I suggested is not clear, please ask me to explain better. Look closely for changes in punctuation. You had a couple of sentence fragments that I changed. I also changed the spelling of the creature to "griffon", which I think is better than "griffin." Both spellings are acceptable, but since "Griffin" is a common surname, I think "griffon" is better when you mean the vulture or the mythical creature. If your teacher prefers "griffin", then spell it as your teacher prefers.
Please ask me to explain better if anything I suggested is unclear. I'll check back in a few minutes, and then again tomorrow. I skipped a line between paragraphs just to make it obvious when I was starting a new paragraph.
Peace be with you.
EDIT: I liked your short story. It is interesting and worth reading. You made errors in grammar, but the story itself is interesting, even a little exciting. I think it is a lot harder to invent a good story than it is to learn grammar. You should be glad that you wrote a good story, and that you only have to improve your grammar.
I recommend a grammar book that is short and very good.
It is well worth buying. You can get it from Amazon for only a few dollars.
This book is simple, which makes it very easy to use.
Many grammar books are awful to read, so people won't even use them.
This book is easy to read,
and it is so useful that you will actually want to use it when you write.
THE TITLE IS: "Write Right!"
AUTHOR: Jan Venolia