I'm preparing a letter for my manager to sign. I don't know how to start the letter, I want the letter to say : I'm John Doe manager of John Smith. And the following is the list of job duties for John Smith who works as a full time employee of XYZ, inc.
I would be thankful if you could help me with that.
The text that you've suggested in your question is very similar to what you should write.
In US business writing, it's important to get straight to the point. Other than greeting and signing off, you don't have to engage in formalities. If you come from a country, such as France, that uses traditional stock phrases in official correspondence, or cultures that value indirectness, writing this way can feel uncomfortable.
You might also feel uncomfortable about other issues related to the subject material. For example, you might have concerns about the employee's performance. If you can't express those issues easily in writing, ask for a "follow-up meeting to discuss the job description and some related concerns" in person.
If your work requires a lot of business correspondence, you can use books that provide example letters. These are useful but limited in scope. I prefer The Big Book Of How To Say It (How To Say It And How To Say It At Work) by Rosalie Maggio. In that book, the author helps you write more authentic correspondence by suggesting some key phrases and providing guidelines to follow.
