My thoughts

Hello everyone! Honestly, I'm feeling very nervous right now and it is precisely because of this letter. I haven't written in English for a long time and I can imagine that there are many, perhaps too many, simple mistakes. Regardless, I do not think that it is the most important of things. The most important thing is having an opportunity to improve my skills. So please, speak up or write to me, but let me know about my mistakes!
Today is a special day. It is the day when I know that I really want to learn English and learn it well! If you find yourself thinking, "What is so special here?," let me explain. Of course, I have always understood that English is a very useful language, but still, I just didn't want to learn it. Why? It was mainly because everyone was always telling me, "You must know English!" And so, similar to how many other people would react, I simply didn't want to do what I had been told to do! Instead, at that time, I learned Korean. There were two main reasons for me to do it: the first, was that I found it to be really interesting and the second, was that I simply did not have to do it. So, yes, I did what I liked better in studying Korean and I was happy.
With the passage of time, however, I have found that my feelings about it are changing.
Today is that day, that special day, when my mind finally decided that English is a beautiful language and I'll be happy to write about it! 
I hope that it will be a good story with a happy ending.
Good luck to everyone in fulfilling your own dream and thank you for reading my letter!

This is a very good start!  I look forward to reading your other compositions in the near future. As to corrections, pay attention to your punctuation and tenses. J.

My thoughts

Hello to (it's fine to leave the "to", however people often say just, "Hi everyone!" or "Hello everyone!") everyone! Honestly, I'm very nervous now, because of this letter. I hadn't write haven't written English for a long time and I suppose that there are many stupid mistakes. But anyway, I think that it is(or "that's") not the most important thing. The most important thing is my opportunity to improve my skills. So please, let me know about my mistakes :))
Today is a unique day. A day when I really want to learn English and know it well! If you think, "What is unique here?", let me explain. Of course, I understand that English is very useful language. But I didn't like it. Why? Just because every time, everyone says, "You must know English". And such as other persons, (it's more natural to say, "Like others", or, "Like other people," )I didn't want to do what I must do. So, for this time I learned Korean. There were two main reasons to do it: it was really interesting and I didn't have to do it. Yes, I did what I liked and was happy.
However, the time run, and our thoughts are changing. (Another way to say this is, "However, with time/as time went on my thoughts changed.")
Today is the day when my mind decided that English is a beautiful language, and I'll be happy to speak on it.
I hope that it will be good story with the a happy ending. ^^
Good luck to everyone in with your dreams and thank you for reading this letter!