Exercise1

I saw the recruitment information regarding the position of foreign trade merchandiser of at your company on in today's "Shenzhen Daily" today.
I want would like to to apply for this position. ...would like to... is more polite. :)
I am 26 years old , and I have been worked as a merchandiser in at TCL Computer Company for the past 4 years.
I have completed the business English course with good results. Which business course?
I hope for you can give me an opportunity to show my capacity in this position. I assure you that if appointed, I will invest all my energy and honesty to your company.
Looking I look forward to hearing from you!

Business communication is challenging because it needs to be clear, concise and precise!  There's always more than one way to achieve this. You're off to a good start.

Exercise1

I saw the recruitment information regarding the foreign trade merchandiser position of available in your company on "Shenzhen Daily" today.

I want to apply for this position.
I am 26 years old, and I have been working as a merchandiser in the TCL Computer Company for 4 years.

I have completed the business English course with good results.
I hope you can give me an opportunity to show demonstrate my capacity abilities in this position. ("Capacity" indicates an amount whereas "abilities" indicates what you can do.)

I assure you that if appointed, I will invest all my energy and honesty to your company.
Looking forward to hearing from you!

Very good. I hope this helps.