You need to set up PayPal Connect first. Go to Jetpack CRM > CRM Settings > PayPal Connect and enter the necessary details:

To get your PayPal API username, password, and signature, you can follow our guide here.
Once you’re all set up with those details and on the PayPal Sync page you’ll see the following page:

Hit Import Now and your customers and transactions will be added to your CRM. You only need to do this once.
Once you’ve done the initial import your CRM will update hourly with any new transactions.