该英语作文呀

Dear sister: How's it going? I had receive you letter yesterday and read it. I think that I can understand your letter .But write the letter have a little diffcult .And I think write the letter in English can improve my English. So
if I have some mistake that please point out my mistake. You're talking about my summer holiday in the letter. I think I have a very substantiate vacation. Because I'll study some subject in the summer holiday .And sometimes I also go to take exercise. In one month I'll visit the Singapore Thailand and with my parents and my grandmother. I think I could have a great time how about you. I read you let

received
had + 动词的过去分词.表示完成时.

And I think it can improve my English if i write a letter in English.

So if I make some mistakes, please point out them.

substantiate是动词.
very后面加形容词,所以要把substantiate改成形容词形式.

Because I'll study some subjects in summer holiday
some 后面加复数,subjects
去掉the

In one month I'll visit the Singapore Thailand with my parents and my grandmother.
Singapore前面的the去掉.
去掉with.

I think I will have a great time.How about you.
要加句号.

If in , I think will have a lot of people get angry with train company.
这句有错,但我不知道你想要表达的意思,所有没改.

I hope you can come back home as quickly as you can.

And sometimes I also go (went)to take exercise.
I think that(去that) I can understand your letter .
You(were) talking about my summer holiday in the letter.
I think I could have a great(good因为great是非常好或者伟大的意思，不应用在这里) time .
应该差不多吧！