To configure the cart to allow PayPal to be used:
Login to cart administration.

Go to "Cart Settings" step #4 "Payment/Gateway Settings".

Fill out the area for PayPal.

Click "Save".
Any orders processed by the shopping cart will make an automatic request to the customer for payment. The customer can follow a standard PayPal process to complete the payment.

If you have a Premier or Business PayPal account you can make the checkout process easier for your customers by doing the following:
Login to PayPal.
Click on "Profile".
Click on "Website Payment Preferences".
Turn on "Auto Return".
If you do not have a PayPal account. You can get one here

Payment Standards From PayPal

Note: We recommend that you do not ship any products until you have verified payment from PayPal.