I'm a newcomer, i have some questions

[cedricxu]

1、I’m a buyer , how can i find someone to do my request, whether the only way is to find, is there a way that sellers will find us forwardly?

2、when i post a request, where i can find my request, whether the request will be in public?

3、how’s the payment, are we should pay before the request finished or after request finished?

[prettytoney]

You can post a request to the buyers requests section. You describe what you need to be done and set your budget then sellers will contact you with their offers.
Other way is to search for a service and write to sellers/order their gigs.
You have to pay upfront but you can get a refund most of the times when you are not happy with the outcome.