what i need to do to apply the working visa?how long it will take

hi my name agustini, iam from indonesia and currently iam in phanthiet vietnam.
i got a job in china and the company in china sent me the documents ( invitation letter and foreigner working license ) to apply for my working visa. So i want to apply my working visa in chinese embassy/ consular in HCMC, what i need to do to apply the working visa?how long it will take, how much the cost and can i use agent to do that for me or i have to come to the embassy? thank you