If you want to ask a person his or her occupation, you can say '你是干什么的？' The pronunciation is nǐ shì gàn shí me de ？

The answer answer normally starts with '我是' (wǒ shì) meaning I am.

If you want to say 'I'm an accountant', you can say 我是会计 (zhí yè wǒ shì huì jì)
If you are an engineer, you can say 我是工程师 (wǒ shì gōng chéng shī)
If you are a teacher, you can say 我是老师 (wǒ shì lǎo shī)