Maybe make a not of the differences in British and American English here too, dang would not be said by someone from the UK. So perhaps it could be expressed as: "Damn, that's hard."

What's the matter? this is used more when you can see there's something wrong with a person How do you feel? this is used for maybe a closer friend or within a medical context, to ask how a person is inside, emotionally as well as a physical thing (if they can feel pain for example)

My Job

Being busy for two weeks,i finished jobs of both container.

Been busy for the last two weeks and finished both container jobs.
It's important to complete each step carefully in order to out Customs successfully.

It's important to complete each step carefully, otherwise there may be problems with customs.
Because this is the intial contact with new business for me.

This is my initial contact with a new business.
After all works were finished.i suddenly felt tired.

Once everything was complete tiredness overwhelmed me.
But this experience will be more handy with facility in future.

This has been a good learning experience for me.

An Imaginary Letter

Hello Rita,

Don't wait for me tonight. After supper I have a date with friends, so go straight home. Could you return Mr.Brown's letter? Aplogize and explain to him the goods he wants are out of stock. I shall contact him when the goods are available.
If he needs any other products, please let me know straight away, thank you.

Best regards,
Xiaohui

It depends on the context, it can be used in a child like way as well as adult. Life isn't fair in general, people earn more money than others, have larger houses etc. So in that context it could be said "Life's not fair!" Likewise a child could have less sweets than his friend and say "That's not fair!" It could be seen as a lame complaint, but for others it is quite a genuine and exact response. For example, the fact palestinians are herded into a tiny piece of overcrowded land by the israelis (current topic!) really isn't fair at all.