Paid Membership Pro LINK Code for Pay Button

Set up Paid Memberships Pro with payment gateway being PayPal Express, but cannot find any documentation or videos on
the code or link needed to add to all my pre-designed buttons on my subscription page that customers click on to purchase. Searched for 2 days and cannot find any documentation anywhere showing the most important step of setting up paid memberships: The pay button.

Do I just build buttons at paypal?

Thanks!