To generate your API Signature,you need to have a Paypal Business account.

• Click the My Account tab.
• Click the Profile subtab.
• Under the Account Information column,click the API Access link.
• Click Request API Credentials.
• Click the API Signature radio button.
• Complete the API Credential Request form by clicking the agreement checkbox and clicking Submit.
• Write down the values listed next to API Username and Password.
• Select the value listed next to Signature Hash,copy it ,and save it to a file or some other location.This is your API Signature.

Your have now generated Your API Username,API Password,API Signature.