Buyers never pay a fee to PayPal. There is, however, a small fee for sellers. They pay a 2.9% transaction fee on the total sale amount plus a $0.30 fee per transaction. There are some exceptions, listed here. If you have a business, see PayPal Merchant Fees for discounted rates and other pricing info.
Transferring money through Paypal is usually free. Sending money to friends and family is free for you and the recipient when you fund the transfer with your bank account or PayPal balance. You can also use a debit or credit card or make an international transfer for a small fee. If you use yoru PayPal balance or a bank account, there is no fee when sending money inside the US. There is a debit/credit card fee that is the same as if you were selling something through PayPal. If you sending money outside the US, there is a small fee of 0.5% to 2%, depending on the destination when fully funded with bank account or PayPal balance. The fee increases to 3.4% to 3.9% if paying with a credit or debit card. For more information about PayPal fees, visit the PayPal website.