To accept payments via Paypal, you'll need a Paypal Business account to get started.
Navigate to the Settings page, found at the bottom of the sidebar.
Select the School icon from your sidebar.
Then go to the Payments page.
From here, press the Connect button next to Paypal. You'll be asked to login to your Paypal and authorise the connection.
When this is complete, you'll be taken back to the payments page and you'll now be able to accept payments through Paypal.