To configure PayPal Payments Pro:

1. Install, Activate, & Enable PayPal Payments Pro Extension
2. From Manage, go to Store > Extensions 
3. Select Payments from Category in Store Extensions section. 
4. Find PayPal Payments Pro and Click Settings Cog Icon
5. Click Test if you're working in a sandbox mode; otherwise, Click Live if you're ready to go live. 
6. Select Automatically Capture Payments to authorize and immediately capture payment for each processed transaction. Select Manually Capture Payments (Authorize Only) if you only want to authorize payment and would rather manually capture funds at a later time. 
7. Provide your test or live credentials: Partner, Vendor, User and Password
8. Click Update

How do I find my Partner, Vendor, User and Password
See: https://manager.paypal.com/