fire away in oral english simply means "begin"
E.g:
1.Fire away,ask me anything you like.
开始吧,请随便向我提问.
2.`I've got a couple of questions I'd like to ask you.' `Right,fire away.'
‘我有几个问题想问你.’‘好,你说吧.’
3.All right,fire away,old chap,I'm listening.
好吧,伙计,说吧,我听着哩.