for PayPal to work you only need to add your email address (API related information is only for PayPal in the mobile app but there is a long process to activate that, including some technical information that you need to submit in API application process and you can do that at a later point).
The difference between Sandbox and Production is that Sandbox is only for TEST transactions and Production is for LIVE payments.
So after you enter your PayPal email just set Payments to Production and you will be ready to take payments through the booking form.
Hope this helps.
Let us know if you have any other questions.