How does Rover work?

I am new to Rover. I want the sitter to be the right match for my dog. My dog is older and has allergies, so I need to ensure that I find a good match for her. When I send a booking request to a potential sitter, is it binding right away? Is my booking request binding as soon as I send it to the sitter? I just have a few questions that I want the sitter to answer before committing. How does this work?

Thank you!