If you would prefer for your clients to be sent to paypal payment directly, skipping amember signup (to avoid having people fill in two forms).
You simply need to add the paypay id of the product to the product in your cart.
Do the following:
aMember cPanel>Products>Manage Products - edit your products in aMember and set up PayPal Button Item Number for each necessary product. (It is necessary so aMember can get idea what product is purchased on PayPal side) You will need to create a paypal payment button with your product details which will endup creating a code. The product number or id you want can be found within the paypal code.
4) Send clients to your shopping cart directly
5) After their purchase they will receive via email from amember the username and password which is auto generated from the payment info. (Your shopping cart behind the scenes tells amember to create the user.)
6) We would recommend you to configure the thank you page after purchase. Set it to a page that explains that they will receive an email with their login and password (you can edit the email template), and maybe tell them were to log in once they receive it, and where to update the password.