Fairly easy and simple.
One detail to know, the seller has to pay a small fee to PayPal. Here is the detailed information taken directly from PayPal's website.
Merchant rate fee schedule
Purchases from $0 USD - $3,000 = 2.96% + $0.30 USD
(purchase payment received monthly) (Fee per transaction)
There a few more perks about using PayPal that I'll write about in a second post.