A PayPal Sandbox account is a test account which you can use to make sure that your online store works fine with PayPal. You can use the sandbox account to make test transactions, and test various PayPal features and settings before you use the actual "live" PayPal account and accept real payments.
To set up a PayPal Sandbox account open the developer PayPal page and click on the button Sign Up Now:
On the page that opens type something in the fields for first and last name, then an email address in the respective field, a password for the account, select a security question and type an answer for it. You don't have to provide your real name, but the email address has to be one that is functional. However, don't use the same email address as the one you plan to use (or you already use) with your "live" PayPal account.
After you you're done click on the Agree and Submit button.
You'll receive an email message with a link in it. So log in to the email account you provided in the registration form, open the message, click on the link, and log in to your PayPal Sandbox account. After you do it you'll see the homepage of your account.
The next thing you should do is to create two test accounts: one business (seller) account, and one personal (buyer) account. To do this click on the link preconfigured account that's on the home page of your PayPal Sandbox account:
On the page that opens select the desired country from the corresponding drop-down menu, choose whether you want this to be a buyer or seller account by marking the respective button. You can't create the two accounts at the same time, so you have to create first one and then the other. Make sure you put some money in the field for Account Balance, so that you can use the account to make test orders. The money, of course, is not real; it's only for testing purposes.
After you're done with the settings click on the button Create Account. Don't forget before that to copy the password.
Then create the second account, and after you have the two accounts (seller and buyer) you can use them for testing.
After the accounts are created you can view their details, like the test credit card information, by clicking on the Test Accounts link on the left. On the page that opens just click on the View Details button for the account (business or personal):
You can use the credit card information that's listed after you click on the View Details button for the personal account, for example, to make test customer orders. When you mark the button for one of the accounts and you click on Enter Sandbox Test Site button that's under the table with the test accounts, you'll be able to enter the particular account and configure its settings.
When you test how your store works with PayPal you will also need the API credentials. To see them just click on the API Credentials link that's on the left side of the PayPal Sandbox account page. The API credentials should look something like this:
Many applications for online commerce, such as Magento and PrestaShop, have the necessary PayPal options integrated into them. You just need to copy the API credentials from your PayPal Sandbox account to the appropriate settings in the particular application.