I did this once at the RWA (Romance Writers of America) national conference I attended, 7 years ago. It's very intimidating, but remember they are speaking with multiple authors in a single day and are used to people being nervous. Practice your pitch so you have it memorized, and have a back-up one in case they're not interested. Definitely have a business card for them, and write the title of your work on the back of it, along with a single tag line for the book. Even if they say no, they'll be more likely to remember you if you pitch to them again via email or Twitter. You won't really have time to ask them much of anything. They're there to hear your pitch. If they say yes, you can clarify what they want to see - first three chapters, full manuscript, etc. And then make sure to actually send it!

I know authors who pitched unfinished manuscripts, got a yes, and never finished the book. Golden opportunity lost forever. And of course, be sure to thank them for their time, even if it's a no. Good luck!!
Adding this because I just realized I didn't completely answer the question. They asked me more about the book I pitched, and of course about my previous writing credits. I had none. And five or ten minutes can be extremely awkward if you don't have a back-up, or fumble around for words when they ask a question about the book, or about the characters or plot in general, and you can't summarize what you want to say. So be sure to really know the works you're pitching, and be able to summarize key points without rambling.
It can also be awkward to sit there with many minutes left and they've just asked if you have anything else to pitch, but you do not. That's why it's best to have a back-up. Makes for a much more graceful exit.
