need J-1 waiever sample letter

hi, friends

I want to apply for J-1 waiver, but I dnot know how to apply for the waiver, and what process that I need to do.

1. Submit application letter to China 大使館, submit letter to DOS to get case number, which one is the first ?
2. I need sample letter from friends, if you have sample letter, could you let me refer to it. you can remove name and private information. i can pay
3. whether or not Dos need recommendation letter from Supervisor or employer ?
4. J-1 to F-1 student, during study, it still needs to waiver?

Thanks lot