...so that concludes my presentation today and I will now be happy to answer any questions you may have.
Er, thank you for such an interesting talk. Could I just ask one question about the plans for a new building that you mentioned at the beginning?
Yes, of course. Fire away.
The expression fire away is an invitation to ask questions about anything you want. It's often used as a friendly and informal reply to someone who has said 'can I ask you something?', and is the same as saying 'go ahead'.
Informal expressions like this can be used occasionally in formal situations, like the presentation example above, to make you sound relaxed, friendly and confident. It's important that your body language matches this message though, so try to smile when you say it!