Here's how: 

1. Log into your Wix Store Manager, AKA "MySite". 
2. Click Settings.
3. Click Accept Payments.
4. Select PayPal.
5. Click the Connect button.
6. Enter your PayPal email address and select Next.
7. Click Agree and connect after you read the terms to grant Wix permission to access your account. 
8. Click the Go back to Wix.com Ltd button.

See also:
Wix Help Center