This is all completely understandable! I have made some grammar, spelling, and vocabulary suggestions.

23/09/2014 Journal

Yesterday, I slept a lot,but my condition was not very good.

I thought think I didn't sleep deeply. I was tired all day.

I couldn't do anything because I woke up late, so I just rested.

Of course I went to English classes. To be honest, I hadn't wanted to go out but, I controlled myself!

Yesterday was not successful to study.

I was not successful at studying yesterday.

I did only my homework at home,whereas but I learned a lot in my class.

I learned 'the article' in the class.

It queit quite helped me. It is tricky grammear to a Korean because we don't use them well in usual general. *

I have enjoyed studying English these_days. I expect that my English skills grow up are improving.

*There are several other ways I could correct that sentence. Here is another option:

It is tricky grammar for Koreans because we don't usually use them well.