How to add payment methods and set PayPal to work with PrestaShop
PrestaShop comes prepackaged with different payment modules. Each payment module makes it possible to add a payment method which customers can choose to use when checking out. To see the available payment modules, log in to the backend of your store, click on the Modules tab and select the section Payments & Gateways. To make a method available install the corresponding module. A Configure button will appear under the module's name after you install it. Click on the button to configure the module's settings.
For some modules such as Bank Wire and Check it's enough to configure their settings to make the respective payment method fully available and functional on the frontend of the shop. There are other modules which are for payment gateways such as PayPal, Moneybookers, Google Checkout, etc. In this case, first you need to create an account in the respective payment gateway and then you have to configure the settings of the corresponding module.
For example, if you want to make payments through PayPal available on your site, first go to the official PayPal site and create an account. It's advisable before that to test your shop with a sandbox PayPal account.
In any case, after you create the account go the Modules tab of your store's backend, find the PayPal module and install it. Then click on the Configure button under the module's name. On the settings page that opens there are three tabs. The first tab (Solution) let's you choose the payment solution (e.g. Payments by credit cards). After that click on the Settings tab. There you can choose whether you want to activate the sandbox mode (for testing purposes) and you also have to copy the API credentials which you can get from your PayPal account ("live" or sandbox). The third tab contains some optional settings. When you're done with the settings click on the Save settings button.
Now, if you did everything correctly, PayPal should be available and functional at the payment step of the check out process.