1st time user - questions on how platform works

I'm a first time user - looking for an email address for support.
I posted what I'm looking for from a freelancer, and it automatically took me to a form for payment.  The payment amount was higher than posted on the profile photo.
How do they come up with how much to charge automatically?
How can I talk/chat with the freelancer to know more about similar projects he may have done or where can I read his testimonials.

I don't want to pay him until I see those things, then we can start the project.  What should I do?